Pada pemetaan f(x)=ax+b,bila f(2)=1dan f(7)=16,maka nilai a-b,adalah... Tolong pake caranya

F(x) = ax + b
F(2) = a.2 + b = 1
F(7) = a.7 + b = 16
2a + b = 1
7a + b = 16
---------------- -
-5a = - 15
5a = 15
a = 3

F(2) = a.2 + b = 1
3.2 + b = 1
6 + b = 1
b = - 5