The reaction of hydrogen with oxygen produces water. 2H2(g)+O2(g)→2H2O(g)

A-How many moles of O2 are required to react with 3.8 mol of H2 ?

Express your answer to two significant figures and include the appropriate units. 

B-How many moles of H2 are needed to react with 4.1 mol of O2 ?

Express your answer to two significant figures and include the appropriate units.

C-How many moles of H2O form when 4.0 mol of O2 reacts?

Express your answer to two significant figures and include the appropriate units.