How do you solve 6) n2+7n+15=5 by factoring?

First, you need to set the equation equal to zero:

n^2 + 7n + 10 = 0

Now we factor. We need to find two numbers that add up to 7 and multiply to 10. 

2 + 5 = 7
2 * 5 = 10

Now, we just need to write this as a polynomial:

(n + 2) (n + 5)
is our answer. 

Hope this helps!