The given function is .

                              (Substitute f(x) = 0)

Apply multiplication property of addition: If a = b then .

And multiply each side by .

Apply zero product property: .

The factors of 15: 5,3 (or) 3, 5 (or) 15, 1 (or) 1,15.

The correct factors are 5, 3 and 15, So m = 5, n = 3.

Then write the factors form .

             (Group terms with common factors)

                     (Factors the grouping terms)

                              (Take out common term )

Apply zero product property: If then a = 0 (or) b = 0.

Solve for first factor .

Apply addition property of equality: If a = b then .

                                 (Add 3 to each side)

Solve for second factor .

Apply subtraction property of equality: If a = b then .

                                (Add 5 to each side)

The roots are 3, and 5.