how does 1 mole of nh2 and 3 moles of nh3 give 20 moles of nh3 I want to see the calculation for that

Example 1.2.8. Stoichiometric Relationship between Moles and Volume In the Haber-Bosch process, hydrogen gas and nitrogen gas react over an iron substrate to produce ammonia, which is used in the production of fertilizer. Given this process, how many litres of NH, can be produced at 27.0 C and 1.0 atm if 20.0 moles of N, are reacted with excess hydrogen? Solution: Start with the balanced equation: N_(g) + 3H, (g) 2NH,(g) According to the balanced equation, 1 mole of N, and 3 moles of H, will give 2 moles of NH3. Similarly, if 20 moles of N, are consumed, 40 moles of NH, can be produced. Use the ideal gas law to find the volume of NH, V=nRT _ (40.0 mol)(0.08206L atm mol-K-1)(300.15K) (1.0 atm) = 990L