4 gross salary of employee

echo enter your salary
read sal
if [[ $sal -lt 15000 ]]
then
    da=`expr $sal \* 90 / 100`
    hra=`expr $sal \* 10 / 100`
else
    da=`expr $sal \* 98 / 100`
    hra=5000
fi
sal=`expr $da + $hra + $sal`
echo your gross salary is $sal