tolong jawab kakak, pakek cara ya kakak, please !!!

Jawaban : A
Cara : f(2) = 2a + b = 11
f(4) = 4a + b = 17
_____________ -
2a = 6
a = 3
f(2) =2(3)+b=11
6+b=11
b = 11 - 6
b = 5
f(7) = 7a + b
= 7(3) + 5
= 21 + 5
= 26