Here is my solution:

<?php
 
$grade = floatval(readline());
gradeInWords($grade);
 
function gradeInWords($grade) {
 
    switch ($grade) {
        case $grade <= 2.99:
            echo 'Fail';
            break;
        case $grade <= 3.49 && $grade > 2.99 :
            echo 'Poor';
            break;
        case $grade <= 4.49 && $grade > 3.49:
            echo 'Good';
            break;
        case $grade <= 5.49 && $grade > 4.49:
            echo 'Very good';
            break;
        default:
            echo 'Excellent';
    }
}