Answer: Choice B (If you need to do questions like this in the future i recommend using the desmos graphing calculator online, inputting the equations and comparing them)
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.
The answer is: 2 times taller than the person
Explanation: 6/15=height of lamp/(15+15); 6/15=height of lamp/30; height of lamp=(30/15)6=2×6, 2 times taller.
(Lamp is 12 feet tall)