four / solution 4.3

<?php

$item1grade = 8 / 10;
$item1weight = 3;

$item2grade = 17 / 25;
$item2weight = 4;

$item3grade = 4.5 / 8;
$item3weight = 6;

$item4grade = 27 / 40;
$item4weight = 5;

$item5grade = 35 / 45;
$item5weight = 5;

$item6grade = 71 / 100;
$item6weight = 10;

$item7grade = 9 / 15;
$item7weight = 12;

$currentScore = $item1grade * $item1weight + $item2grade * $item2weight + $item3grade * $item3weight + $item4grade * $item4weight + $item5grade * $item5weight + $item6grade * $item6weight + $item7grade * $item7weight;

$currentGrade = (100 * $currentScore) / ($item1weight + $item2weight + $item3weight + $item4weight + $item5weight + $item6weight + $item7weight);

$currentLetter = "f";
$currentGrade >= 90 && ($currentLetter = "a+");
$currentGrade < 90 && $currentGrade >= 80 && ($currentLetter = "a");
$currentGrade < 80 && $currentGrade >= 70 && ($currentLetter = "b");
$currentGrade < 70 && $currentGrade >= 60 && ($currentLetter = "c");
$currentGrade < 60 && $currentGrade >= 50 && ($currentLetter = "d");

print_r("your current grade is " . $currentGrade . "%, which is " . $currentLetter . ".\n\n");

// ($currentScore + 75x) / 120 = 70% where x is required for b
// ($currentScore + 75y) / 120 = 50% where y is required for d

$needForB = (0.7 * 120 - $currentScore) / 0.75;
$needForD = (0.5 * 120 - $currentScore) / 0.75;

print_r("to get a b, you need an average of " . $needForB . "% on the rest of your semester.\n\n");
print_r("to get a d, you need an average of " . $needForD . "% on the rest of your semester.\n\n");