hosphoric acid, a mild acid used among other things as a rust inhibitor, food additive, and etching agent for cavity repair by dentists, can be made from elemental phosphorus in a two step process. In the first step, phosphorus and oxygen react to form diphosphorus pentoxide:

→+P4s 5O2g 2P2O5g
In the second step, diphosphorus pentoxide and water react to form phosphoric acid H3PO4:

→+P2O5g 3H2Ol 2H3PO4l
Suppose the yield of the first step is 69.% and the yield of the second step is 60.%. Calculate the mass of phosphorus required to make 6.0kg of phosphoric acid.

Be sure your answer has a unit symbol, if needed, and is rounded to 2 significant digits.