Any help would be appreciated!

A person is lying on a diving board 2.50 m above the surface of the water in a swimming pool. She looks at a penny that is on the bottom of the pool directly below her. To her, the penny appears to be a distance of 5.50 m from her. What is the depth of the water at this point?

Not sure how to approach this problem. Do I use the index of refractions of water and air? I also tried doing : (-s')/s= y'/y but I got stuck.