pake cara nomer 7 dan 9 ya..

7. a. f(4)= 4a + b = 5
f(-2) = -2a + b = -7
eliminasi
menjadi
6a = 12
a = 12/6
a = 2
4a + b = 5
4.2 + b = 5
8 + b = 5
b = 5-8
b -3

9.???

(maaf kalau salah)