Diketahui fungsi f(x)=ax+b jika f(2)=-2 dan f(3)=13, tentukan nilai f(4)

f(3)=3a+b=13
f(2)=2a+b=-2
-------------------- -
a=15
2(15)+b=-2
b =-2-30
b = -32
f(x)=15x-32
f(4)=15. 4-32=60-32=28