Nomer 12,13,14 itu caranya gimana ya?

12. berat safi = x
naufal = y
x = 3+y
x+y = 109
(3+y)+y = 109
3+2y= 109
2y= 106
y = 53

x= 3+y
= 3+53
= 56

14. f(x) = 2x - 5
f(b) = 2b - 5
7 = 2b - 5
2b = 12
b = 6

14.
f(x) = 2x - 5
jika f(b) = 7
maka
2b - 5 = 7
2b = 7 + 5
2b = 12
b = 6
maaf no 13, aku lupa rumusnya