Jawab yang nomor 18 ya...

f(x) = 5x + n
f(-1) = 5.-1 + n = 2
n = 2 - (-5)
n = 7

f(4)= 5. 4 + 7
= 27

f(1) = 5.1 +7
= 12

f(4) - f(1) = 27 - 12 = 15
Jawabannya D