need code break down explaination

Question

$arg = 5;
$result = 0;

for($i=0; $i<$arg; $i++) {
$result = $result + 4 ;
}
echo $result;

how is this outputting 20 ?

Answer 1

number of times the for loop runs
inital value of result is 0

for (5 times){
4 is added to result
}
result is now 20 (4+4+4+4+4)

Answer 2

The for loop runs 5 times, because $i takes values 0, 1, 2, 3 and 4. In each of these 5 iterations, you add 4 to $result, which had an initial value of 0. So finally $result is equal to 0+5*4=20.