Tolong dibantu kak soal no 14

F(x) = (5x – 1)/(4x + 3)
y = (5x – 1)/(4x + 3)
y(4x + 3) = 5x – 1
4xy + 3y = 5x – 1
x(4y – 5) = -3y – 1
x = (-3y – 1)/(4y – 5)
(f(x))^-1 = (-3x – 1)/(4x – 5)
(f(p))^-1 = 4
(-3p – 1)/(4p – 5) = 4
-3p – 1 = 4(4p – 5)
-3p – 1 = 16p – 20
-1 + 20 = 16p + 3p
19 = 19p
p = 1