<?php

$total = 0;
$booster3 = 200;
function rocketThrust1($booster1, $booster2)
{
    global $total;
    $total = $booster1 + $booster2;
}
function rocketThrust2($booster3 = 200)
{
    global $total;
    $total = $total + $booster3;
}
rocketThrust1($booster1 = 50, $booster2 = 100);
echo 'Rocket thrust is currently stable at ' . $total . ' newtons';
rocketThrust2($booster3 = 200);
echo 'Rocket thrust is currently stable at ' . $total . ' newtons';
<?php

$total = 0;
$subtotal = 0;
function rocketThrust1($booster1, $booster2)
{
    global $subtotal;
    $subtotal = $booster1 + $booster2;
}
function rocketThrust2($booster1, $booster2)
{
    global $total, $subtotal;
    $total = $subtotal + $booster1 + $booster2;
}
rocketThrust1($booster1 = 50, $booster2 = 100);
echo 'Rocket thrust is currently stable at ' . $subtotal . ' newtons';
rocketThrust2($booster1 = 100, $booster2 = 100);
echo 'Rocket thrust is currently stable at ' . $total . ' newtons';