Answer:
13.00 g
Step-by-step explanation:
To solve this problem, you need to understand the law of conservation of mass. This law means that whatever amount you start out with is what you should have at the end. The amount may be in different forms, but that amount is still there.
If you produced 10.00 g of B and 3.00 g of A, you should have started out with 13.00 g of AB.
10.00 + 3.00 = 13.00