Bubble shooter game mechanics

Hi everybody,
I want to recreate the bubbleshooter game but I can’t figure out how to get a ‘bullet’ moving towards my mouse, which will be the direction of the bullet. I tried using the formula y=ax+b and also tried to do it with vectors but nothing seems to work.
Could someone give me some advice?

rembound has a great tutorial i used many years ago. you can check it out here