How many moles of h2 are need to produce 11.21 g of nh3

First of all, you should write down a balanced equation for the reaction
3H2 + N2 > 2NH3
convert  from grams of NH3 moles NH3moles H2g H2

11.21 gNH3 / ( 17g/ mol NH3)* (3 moles of H2/ 2 moles of NH3) * (2 g H2/ mol H2) 

Ibelieve the answer 4 moles