Fm(x) = x2 + 3 and n(x) = 5x + 9, which expression is equivalent to (mn)(x)? a.5x3 + 9x2 + 15x + 27 b. 25x2 + 90x + 84 c. x2 + 5x + 12 d. 5x2 + 24

To find mn(x), we multiply the given functions m(x) and n(x), to get (x^2 + 3)(5x + 9) = 5x^3 + 9x^2 + 15x + 27. No further simplification is necessary.

This is choice A. Note that by inspection, it can be seen that m(x) * n(x) should result in a cubic expression, and only A has a cubic term 5x^3, while the rest only have up to quadratic (x^2) terms.