Write into a single logarithm log b (X+1) + log b (X-8)

To solve, use properties of logs, specifically log (u) + log (v) = log (uv). This makes your equation logb (x+1) + logb (x-8) = logb ((x+1) (x-8)), which can be made into logb (x^2-7x-8) by expanding the factored form.