Question

f (x) = 5x – 4, g(x) = x2 + 3x – 8

Evaluate g( f(x) ) for x = 3.

g( f (3)) = g

Answer 1

$g(f(3))=(5\cdot3-4)^2+3(5\cdot3-4)-8=121+3\cdot11-8=146$

Answer 2

$f\left( x \right) =\quad 5x-4\\ g\left( x \right) =\quad { x }^{ 2 }+3x-8\\ g\left( f\left( x \right) \right)$ 
for x=3

$f(3)=\quad 5\cdot 3-4\\ f(3)=15-4\\ f(3)=11\\ g(f(3))=g(11)\\ g(11)=\quad { 11 }^{ 2 }+3\cdot 11-8\\ g(11)=\quad 121+33-8\\ g(11)=146$

I hope this was what you asked for.