Please explain each response to each prompt using physics terms/ideas/formulas/proofs. I would like to check my own work

How deep is that well? You come across a well, and you want to gure out. how deep it is. You drop a pebble and measure that it takes 3.2s before you hear a splash. It's too dark to see the bottom, so you can't see the splash to know when it actually hit the bottom. How deep is that well