It appears that you multiplied exponents while finding the product of the two functions. When multiplying terms with the same base, multiply the coefficients and add the exponents. Start with:

$\displaystyle{\left({f{\cdot}}{g}\right)}{\left({x}\right)}={f{{\left({x}\right)}}}\cdot{g{{\left({x}\right)}}}={\left({3}{x}\right)}{\left({{x}}^{{2}}-{5}{x}-{9}\right)}\usepackage{cmbright}\Huge\$

Use the distributive property.