help guys! mtk! tentang fungsi

f (x)=ax+b
f(2)=a(2)+b=1
       2a+b=1
f(4)=a(4)+b=7
       4a+b=7

2a+b=1
4a+b=7
--------------  -
-2a=-6
   a=3

sub a=-3
4(3)+b=7
12+b=7
     b=-5
nilai a+2b= 3+2(-5)=3-10= -7

f(2) = 1 = 2a+ b = 1
f(4) = 7 = 4a + b = 7
---------------- -
-2a = -6
a = 3
● 4a + b = 7
4(3) + b = 7
12 + b = 7
b = 7-12
b = -5
● a + 2b
= 3 + 2(-5)
= 3 -10
= -7 (a)
*maaf kalau salah