First, find f(x):
f(x) = 5x^4
Next, find g(f(x)) by substituting f(x) into g(x):
g(f(x)) = 15(f(x)) + 10
Substitute the expression for f(x) into g(x):
g(f(x)) = 15(5x^4) + 10
Now, simplify the expression:
g(f(x)) = 75x^4 + 10
So, g(f(x)) is equal to 75x^4 + 10.