Solving for a react using a chemical equation

Question

Ammonium phosphate ((NH4)3PO4)is an important ingredient in many fertilizers. It can be made by reacting phosphoric acid (H3PO4)with ammonia (NH3).

What mass of ammonium phosphate is produced by the reaction of 6.9g of ammonia?

Be sure your answer has the correct number of significant digits.

Answer 1

Balanced equation: 3NH3 + H3PO4 -- > (NH4)3PO4

Molecular masses of each component: 

NH3 = 17.03g/mol,  H3PO4 = 98.00g/mol, (NH4)3PO4 = 149.09g/mol

Conversion factor to calculate grams (NH4)3PO4 produced:

1 x Molecular mass (NH4)3PO4 / 3 x molecular mass NH3 x grams NH3 used.

Grams (NH4)3PO4 produced = 1 x 149.09 / 3 x 17.03 x 6.9 = 20.14 grams (NH4)3PO4

 Produced.

As the mass of NH3 is given to two sig figs, the answer should be 20. grams.