Expand and simplify (x+4)(x+5).

First, we need to expand the brackets out. To do this first times the x term in (x+4) by everything in the other brackets. We need to make sure to do this term by term. This will give us x^2+5x. Next, we now need to do the same with the +4 term. So, times 4 by everything in other brackets. Once more do this term by term. This gives 4x+20. Now we put both these parts together to give x^2+5x+4x+20.The final part is to simplify x^2+5x+4x+20. The only parts we can do this with is the ones with the same x next to them. So, this means that x^2 and 20 stay the same, but we can add 5x and 4x together to give 9x. As a result, our final answer is x^2+9x+20.