I am assuming you really don't want the product of those functions; you want to know what the "function of a function", f{g(x)],is. To get that, substitute g(x) for x in the f(x) expression.
f(x) = 3 sqrt(x+1)
g(x) = x^3 + 1
f{g(x)] = 3 sqrt(x^3 +1 + 1)
= 3 sqrt(x^3 +2)
Find f X g
3 sqrt of x+1 X x^3+1
2 answers
if 2^x=3 whats does 4^-x equal