If m(x) = x2 + 3 and n(x) = 5x + 9, which expression is equivalent to (mn)(x)?

For this case we have the following functions:
 
 Multiplying both functions, we obtain an expression equivalent to (mn) (x).
 We have then:
 
 Substituting values we have:
 
 Rewriting the expression we have:
 
 
 An expression that is equivalent to (mn) (x) is:
 

Are there any statements?