hokage

In terms of better deal, we know that we want less money per hour.  to find this we compute danny's cost per hour and martin's cost per hour of lessons and compare the 2.  
Danny: 35/3 = 11.67 dollars/hour
martin: 24/2 = 12 dollars/hour
this means Danny has the better deal since his cost per hour is lower.

note that we could have also computed how many hours of lesson per dollar and in that cause the bigger number would be considered the better deal.
Danny: 3/35 = 0.086
martin: .083
this means danny has the better deal (like before!) because you get more hours of swimming lessons with 1 dollar.

although i think to choose a swim coach we have to look at his abilities as well not just how much he charges XD...sorry i got carried away.