Tolong bantu mr.crussader ^_^

f(x) = ax + b
f(3) = 15 ----> 3a + b = 15
f(-2) = 10 ----> -2a + b = 10
                         ------------------- (-)
5a = 5
a = 1

substitusi,
3a + b = 15
3(1) + b = 15
3 + b = 15
b = 15 - 3
b = 12

b) f(x) = ax + b = x + 12
c) f(7) = 7 + 12 = 19