Diketahui f(x) = ax + b. Jika f(-1) = 9 dan f(2) = 3, maka nilai f(15) adalah... Mohon dijawab pake cara ya. Makasih

f(-1) = -a + b =9
f(2) = 2a + b = 3

eliminasi b
-a -2a = 9-3
= -3a = 6
a = 6/ (-3) = -2

subtitusi a
2a + b = 3
2(-2) + b = 3
-4 + b = 3
b = 3+4 = 7

f(15) = 15a + b
15(-2) + 7
-30 + 7
= -23

f(x) = ax + b
f(-1) = -1a + b = 9
f(2) = 2a + b = 3
------------------------- -
 -3a = 6
a = -2

(2 x -2) + b = 3
-4 + b = 3
b = 3 + 4
b = 7

f(15) = 15a + b = ?

(15 x -2) + 7 = -30 + 7 = -23