foreach_hell.php

<?php

$totalScore = 0;

foreach ($exam as $value) {
    foreach ($value->mocks as $mock) {
        foreach ($mock->items as $item) {
            $totalScore += (int)$item->ext->score;
        }
    }
}

$totalScore = collect($exam)->flatMap->mocks->flatMap->items->reduce(function ($c, $v) {
    $c += $v->ext->score;

    return $c;
}, 0);

// ---------------------------------

$totalScore = 0;

foreach ($exam as $value) {
    foreach ($value->mocks as $mock) {
        foreach ($mock->items as $item) {
            $totalScore += (int)$item->score;
        }
    }
}

$totalScore = collect($exam)->flatMap->mocks->flatMap->items->sum->score;