Can you solve this problem?

2a+b/(a-b)(a-2b) - a+4b/(a-b)(a-3b) - a-7b/(a-2b)(a-3b)

Rewrite them with a common denominator of (a-b)(a-2b)(a-3b) and combine terms in the numerator. You have not used parentheses in your numerators, but you need to use them to clarify what the numerators are.