Dear children, if you know that A equals 8, you can get the answer by substituting 8 into the formula. Please have a look.

2*a=2*8= 16

a+2=8+2= 10

a-2=8-2=6

A/2=8/2=4 (your topic is box, I think it should be division, because you have addition, subtraction, multiplication and division)

hope this helps