Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - drupal/core 8.8.x-dev requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.x-dev requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.6 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.5 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.4 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.3 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.2 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.1 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.0-rc1 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.0-beta2 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.0-beta1 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.0-alpha2 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.0-alpha1 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - drupal/core 8.7.0 requires ext-gd * -> the requested PHP extension gd is missing from your system.
    - Installation request for drupal/core ^8.7.0 -> satisfiable by drupal/core[8.7.0, 8.7.0-alpha1, 8.7.0-alpha2, 8.7.0-beta1, 8.7.0-beta2, 8.7.0-rc1, 8.7.1, 8.7.2, 8.7.3, 8.7.4, 8.7.5, 8.7.6, 8.7.x-dev, 8.8.x-dev].

  To enable extensions, verify that they are enabled in your .ini files:
    - /etc/php/7.2/cli/php.ini
    - /etc/php/7.2/cli/conf.d/10-mysqlnd.ini
    - /etc/php/7.2/cli/conf.d/10-opcache.ini
    - /etc/php/7.2/cli/conf.d/10-pdo.ini
    - /etc/php/7.2/cli/conf.d/15-xml.ini
    - /etc/php/7.2/cli/conf.d/20-calendar.ini
    - /etc/php/7.2/cli/conf.d/20-ctype.ini
    - /etc/php/7.2/cli/conf.d/20-dom.ini
    - /etc/php/7.2/cli/conf.d/20-exif.ini
    - /etc/php/7.2/cli/conf.d/20-fileinfo.ini
    - /etc/php/7.2/cli/conf.d/20-ftp.ini
    - /etc/php/7.2/cli/conf.d/20-gettext.ini
    - /etc/php/7.2/cli/conf.d/20-iconv.ini
    - /etc/php/7.2/cli/conf.d/20-json.ini
    - /etc/php/7.2/cli/conf.d/20-mbstring.ini
    - /etc/php/7.2/cli/conf.d/20-mysqli.ini
    - /etc/php/7.2/cli/conf.d/20-pdo_mysql.ini
    - /etc/php/7.2/cli/conf.d/20-phar.ini
    - /etc/php/7.2/cli/conf.d/20-posix.ini
    - /etc/php/7.2/cli/conf.d/20-readline.ini
    - /etc/php/7.2/cli/conf.d/20-shmop.ini
    - /etc/php/7.2/cli/conf.d/20-simplexml.ini
    - /etc/php/7.2/cli/conf.d/20-sockets.ini
    - /etc/php/7.2/cli/conf.d/20-sysvmsg.ini
    - /etc/php/7.2/cli/conf.d/20-sysvsem.ini
    - /etc/php/7.2/cli/conf.d/20-sysvshm.ini
    - /etc/php/7.2/cli/conf.d/20-tokenizer.ini
    - /etc/php/7.2/cli/conf.d/20-wddx.ini
    - /etc/php/7.2/cli/conf.d/20-xmlreader.ini
    - /etc/php/7.2/cli/conf.d/20-xmlwriter.ini
    - /etc/php/7.2/cli/conf.d/20-xsl.ini
  You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.