How do you solve this problem?

The avera&e (aritmeticmean)of x and y is 5 and the avera&e of x, y, and z is 8. What is the value of z?

(a)19
(b)14
(c)13
(d)11
(e)3 I solved it by addin 8+5=13
So I chose (c)13. But it's wron& and the answer is (b)14. How did they arrive at that answer?????

You should solve it by two fives + z=24

why do i have to solve it this way?

5+5+z=24
10+z=24
-10 -10
z=14