"In the lab, Bill has two solutions that contain alcohol and is mixing them with each other. He uses 100 mL less of solution A than solution B. Solution A is 17% alcohol and Solution B is 20% alcohol. How many mL of Solution A does he use, if the resulting mixture has 94 mL of pure alcohol?"

Could anyone help me with this? I only need to get 3 more of these problems right and then I'll be done. But I am really stuck.