Jika f(x) = x / 3x + 1 dan (fog)(x) = 4x. Tentukan g(x)

f(x)= x /(3x+1)
fog(x) = 4x
f{g(x)} = 4x
g(x) / ( 3. g(x) + 1) = 4x
4x ( 3. g(x) + 1) = g(x)
12 x  g(x) + 4x  = g(x)
12x . g(x) - g(x) =  - 4x
g(x) { 12x - 1 } =  - 4x
g(x ) = - 4x / (12 x - 1)