Hydrogen gas problem using ideal gas law

Consider a vehicle powered by hydrogen gas.

a. About 3.1 kg of H2 is required for a vehicle to have a 500 km range. Assume ideal gas behavior and a storage tank of 60 L (a comparable size to conventional gasoline vehicles). What tank pressure atm might one expect at 25 degrees celsius?

b. Since their discovery in 1991, tiny graphite-like cylinders known as nanotubes have been widely researched. These nanotubes (1-3 nm in diameter) have high tensile strength, high electrical conductivity, and a high surface area. Hydrogen can readily abosrb onto these carbon fibers. The textbook indicates that these nanotubes can absorb three times their weight in H2. What minimum amount of this carbon allotrope (g) would be needed to reduce the tank pressure in the above hydrogen-powered vehicle to 20.0 atm?

I'm pretty sure I'm supposed to use the PV = nRT, but again I'm having trouble setting it up, and was curious if you could give me a step by step solution(s) so I can apply it to my other problems.  Thanks!