Answer: x cannot equal 4/5 (3rd choice)
Explanation:
f(g(x)) = f(5x-4)
plug 5x-4 into all values of x in the f(x) equation
f(5x-4)= ((5x-4) - 3))/ (5x-4)
f(5x-4) = (5x-7)/(5x-4)
set denom = 0 and solve for x to find domain
5x-4 = 0
5x = 4
x = (4/5)
x cannot equal (4/5)