You can put this solution on YOUR website! If this is supposed to be f(g(3)) then substitute x=3 into the equation for g(x) to find g(3).
g(x)=5x - 1
=5 x 3 - 1
=14
Now substitute 14 into the equation for f(x) to to find f(14)
f(x)= x^2 (where ^2 means x squared)
=14 ^ 2
=196