<?php
if ($stmt = $link->prepare("SELECT `Balance` FROM table WHERE `username` = ?")) {
    $stmt->bind_param("s", $username);
    $username = '...';
    if ($stmt->execute()) {
    $result = $stmt->get_result();
    if ($result->num_rows > 0) {
        while ($row = $result->fetch_assoc()) {
            echo $row['Balance'];
        }
    }
}