Array reduce, first add integers.

The array is:

Array ( [0] => 2 [1] => 4 [2] => 6 [3] => 8 )

About to carry out the array reduction.
Running sum: ... next value: 2 ... returns: 2
Running sum: 2 ... next value: 4 ... returns: 6
Running sum: 6 ... next value: 6 ... returns: 12
Running sum: 12 ... next value: 8 ... returns: 20

The results is: 20