using stoichiometric ratios and the ideal gas law the ratio of substances can be determined:
NxHy -> AN2 + BH2
10L : 10L : 20L
1 : 1 : 2
therefore, a = 1, b = 2
therefore x = 2, y = 4
therefore hydrazine is N2H4
for part B you use the combined gas law and the molar mass of the substance...