Question

Here's the question.
"Fertilizers are generally marked with 3 numbers to indicate N, P, and K content. The Hyponex you analyzed is a 7-6-19 plant food. Phosphorus content in fertilizeris generally reported in %P2O5. Convert your %PO4 to %P2O5 and compare your result with the %P2O5 indicated on the label."
If someone could just tell me the usual way you convert %PO4 to %P2O5, that would help so much!Thanks!