pake caranya ya say..

f(-2) = a(-2)+b = -5
f(3) = a(3)+b = 15
............,........................ —
............ -5a = -20
............ a = -20:(-5) = 4

3a+b = 15
b = 15-3(4) = 15-12= 3

f(-5)+f(1) = 4(-5)+3 + 4(1)+3 = -20+3+4+3 = -10