how do you solve x2+5x+6

You cannot SOLVE it because there is no equal sign.  :)

I'm not quite sure what you're asking, but I believe you mean to simplify it. You need to find like terms, which are parts of a question that are similar enough to add. 4 and 5 would be like terms, and you could add them to get 9. In a similar way, x2 and 5x are two similar terms. Try to visualize something like boxes or silverware in a droor to help you. Simply, 2x + 5x would equal 7x. Since we don't know what "x" equals, the simplest form of that equation is 7x+6.