3(a-b)-a+b ????
3(a-b)-a+b
first, distribute (because of PEMDAS, multiplication comes before addition and subtraction [you can't do anything inside of the parentheses])
3a-3b-a+b
then, combine like terms
3a-a-3b+b
2a-2b
Simplify
2(a-b)
+30 
