The 21.3 g sample of phosphorus (V) oxide was dissolved in 326.7 ml of hot water, the resulting solution was divided into two parts in a ratio of 1: 2 by mass. Eight grams of dry sodium hydroxide was added to the two solutions obtained, and 7.1 grams of P2O5 was added to the small mass solution.

A) What is the mass of salt (g) in the small mass solution?

B) What is the mass fraction (%) of salt in the large mass solution?

The answers are A) 24, B) 10. Please explain in detail!