Diketahui fungsi f(x) =12-3x dengan nilai f(a) =48.Nilai a adalah..

f(x) = 12 - 3x
f(a) = 48

12 - 3a = 48
12 - 48 = 3a
-36 = 3a
-36 : 3 = a
-12 = a

f(x) = 12 - 3x
f(a) = 12 - 3a

12 - 3a = 48
-3a = 48 - 12
-3a = 36
a = 36/-3
a = -12