您应该将返回值存储在一个变量中：

You should simply store the return value in a variable:

$deliveryPrice = getDeliveryPrice(12);
echo $deliveryPrice; // will print 20

$ deliveryPrice 上面的变量是函数内部的不同的变量，而不是 $ deliveryPrice 。由于变量范围，后者在函数外部不可见。

The $deliveryPrice variable above is a different variable than the $deliveryPrice inside the function. The latter is not visible outside the function because of variable scope.