Solve the all given parts of following problem:

Problem: You are designing a space station and want to get some idea how large it should be to provide adequate air for the astronauts. Normally, the air is replenished, but for security, you decide that there should be enough to last for two weeks in case of a malfunction.

Part A: Estimate how many cubic meters of air an average person breathes in two weeks. A typical human breathes about 12 L per breath. =200 cubic meters

Part B: If the space station is to be spherical, what should be its diameter to contain all the air you chosen in part A (200 cubic meters)?

I know the correct answer for above problem but explain how to get this answer! Thanks.