Using 50 gal per minute pumps how long will it take to fill a basement that is 16 inched in depth

For a total of 14681.9 gallons. At 50 gallons per minute it will take 294 minutes which is about 5 hours and hence with 2 pumps about 2.5 hours.

Those TWO pumps together work at a rate 100 gallons per minute.

You have basement dimensions, but to get volume as gallons, you need to know:
This is wrong: 231 cubic feet = 1 gallon

Know these: 231 cubic inches = 1 gallon, 12 inches = 1 foot

, cubic feet, the volume of water in the basement - which seems to be given in two sections.

You would use a uniform rates formula like RT=V for rate, time, volume.
You would use it as T=V/R.