tolong yaa yang no 8 pakai cara.. makasii:)

diket : f(x) =3x-11
f(a) =-20
dit. : nilai a...?
jwb :
f(x) =3x-11
f(a) =3.a-11
f(a) =3a-11= -20
=3a = -20+11
=3a = -9
= a = -9/3
= a = -3