Tolong di jawab yaa pake cara jugaaa makasih :)

f(x) = ax+b
f(1) = a(1)+b = 11
a + b = 11
f(4) = a(4)+b = 20
4a + b = 20

Eliminasi
4a + b = 20
a + b = 11
------------------------ (dikurangi)
3a = 9
a = 9/3
a = 3

Subsitusi
a + b = 11
3 + b = 11
b = 11-3
b = 8

Jadi
f(-1) = ax+b
= 3(-1) + 8
= -3 + 8
= 5

Semoga bermanfaat :)

Jawabannya ada di foto yaaaaaaaaaaaaaaaa