The answer for that is A. 40 cubic in
I'm assuming you meant to say f(x) = 3x^2. If that assumption is correct, then the degree is found by multiplying the leading terms from both f(x) and g(x). The leading terms are 3x^2 and 4x^3
3x^2*4x^3 = (3*4)*(x^2*x^3) = 12x^(2+3) = 12x^5
The exponent of that result is 5, so the degree of (f*g)(x) is 5
Answer: 5
