tolong dibantu no yg saya lingkar yaa

16. f(x) = 15 - 2x
f(b) = 15 - 2b = 7
-2b = -8
b = 4
18. 2x - 6y = 10
2x - 5 = 9
___________ _
y = -1
2x - 5 (-1) = 9
2x - (-5) = 9
2x = 4
x = 2

3x + 2y = 3(2) + 2(-1) = 6 -2 = 4