tolong jawab 15&16 guys pekek caranya☺ mksh

15. f(x) = 3x - 1
f(a + 1) = 11
3(a + 1) - 1 = 11
3a + 3 - 1 = 11
3a + 2 = 11
3a = 9
a = 3
Jawaban: D

16. f(3x - 1) = 6x + 3

3x - 1 = -5
3x = -4
x = -4/3

f(3(-4/3) - 1) = 6(-4/3) + 3
f(-4 - 1) = -8 + 3
f(-5) = -5
Jawaban: C