A large pile of coins consists of pennies, nickels, dimes, and quarters. if the pile contains only 15 quarters and only 20 dimes but at least 30 of each other kind of coin, how many collections of 30 coins can be chosen?

If the bank has only quarters and dimes, and its total amount of coins is 250, then be x the amount of quarters it has, it will have 250-x dimes.

A quarter is worth 0.25$, a dime is worth 0.10$ and the 250 coins together are worth 39.25$.