10. Diketahui rumus f(x) = 4x - 9

Saya bantu jawab ya :D

MATEMATIKA
Fungsi

f(x) = 4x - 9

f(a) = 4a - 9 = - 21
4a = - 21 + 9
4a = - 12
a = - 12 ÷ 4
a = - 3

f(a + 21) = f(a + 21) = 4(a + 21) - 9
f(a + 21) = f(- 3 + 21) = 4(- 3 + 21) - 9
f(a + 21) = f(18) = 4(18) - 9 = 72 - 9 = 63
f(a + 21) = 63

Jadi, f(a + 21) = 63
Jawaban : (A)