Tolong pke cara???.....

[tex]f(x) = - ax + b \\ f(2) = - 2a + b = 1 \\ f(4) = - 4a + b = 7 \\ f(2) - f(4) = > 2a = - 6 = > a = \frac{ - 6}{2} = - 3 \\ \\ - 2a + b = 1 \\ - 2( - 3) + b = 1 \\ 6 + b = 1 \\ b = 1 - 6 \\ b = - 5 \\ \\ a + 2b = - 3 + 2( - 5) = - 3 - 10 = - 13[/tex]
jawabannya A