Ok, here goes again. This problem is difficult for me. In deep-sea diving, the pressure exerted by water plays a great role in designing underwater equipment. If at a depth of 10 feet there is a pressure of 21lb/in (squared), and at a depth of 50 feet there is a pressure of 75lb/in (squared), write an equation giving a relationship between depth and pressure. Use this relationship to predict pressure at 100 feet. I've tried finding the slope and using that to solve the equation but it didn't work. Neither did the substitution method.

Question

Ok, here goes again.  This problem is difficult for me. In deep-sea diving, the pressure exerted by water plays a great role in designing underwater equipment. If at a depth of 10 feet there is a pressure of 21lb/in (squared), and at a depth of 50 feet there is a pressure of 75lb/in (squared), write an equation giving a relationship between depth and pressure. Use this relationship to predict pressure at 100 feet.  I've tried finding the slope and using that to solve the equation but it didn't work. Neither did the substitution method.