1) Let F denote Brandon Filop's pennies and W denote Billy Wang's pennies.

...[1]

...[2]

By subtraction we have

So

2) The number of digits of a number N is

So the number of digits in is

Then get out a calculator and that's 1993 digits.

3)

4)

5) The rectangular tank contains of water.

The volume of the cylindrical tank is where h is the height.

Then we substitute in 385: