calculus

f(x) = sqrt(x) - 4

g(x) = x^2 -4

f * g

= f(g(x))

=f(x^2 - 4)

= sqrt(x^2 - 4) - 4

g * f

= g(f(x))

= g(sqrt(x) - 4)

= (sqrt(x) - 4)^2 - 4

simplify . . .

this is hardly calculus by the way. This might qualify as early pre-calculus, but it's likely algebra II.