First, you combine like terms. I would start by circling the term and the sign in front of it. (A term is a piece separated by an addition/subtraction sign.) You can only combine terms with the same variable. 4.8a-2.1a-6.3b+7b is the same as your equation, just rearranged. Then, subtract (4.8a-2.1a) which is 2.7a. Add (-6.3b to 7b) The answer is 0.7b. If you have any questions, you can message me!