Çözüldü Composite Functions - Polynomials - Undetermined Coefficients Rule

https://i.ibb.co/pQv2z8z/fgx.png

As g must be a first degree polynomial, g(x) = ax + b then (f o g)(x) = f[ g(x) ] = 7 - 4ax - 4b = -1 and applying Undetermined Coefficients Rule;
-4a = 0 ⇒ a = 0
7 - 4b = -1 ⇒ b = 2
So, g(x) = 0·x + 2 = 2.

Other solutions and explanations (I have not read.):
https://www.reddit.com/r/Sat/comments/93ljm3/sat_math_level_2_subject_test_practice_question/