Marty has a right circular cylindrical pool of diameter 12 feet and his neighbor, Rusty, has a right circular cylindrical pool of diameter 18 feet. If the depths of the pools are equal, then the volume of water in Rusty’s pool is how many times that in Marty’s pool?

1. 1.5
2. 2.25
3. 2.5
4. 4
5. 4.25