Diketahui f(x)=ax + b, f(-2)=25 dan f(1)=-20 maka nilai a dan b adlh?

f(x) = ax + b
f(-2) = 25
f(1) = -20
a dan b

-2a + b = 25
a + b = -20
___________-
-3a = 45
a = -15

a + b = -20
-15 + b = -20
b = -20 + 15
b = -5