Final answer:
To make x² + 6x + c a perfect square trinomial, the value of c is 9.
Step-by-step explanation:
To make x² + 6x + c a perfect square trinomial, we need to determine the value of c.
A perfect square trinomial can be factored into the square of a binomial, where the binomial has the form (x + a)^2.
By comparing x² + 6x + c with (x + a)^2, we can see that a = 3.
Therefore, the value of c that makes x² + 6x + c a perfect square trinomial is c = 9 (since 3^2 = 9).