Tetrаphоsphоrоus hexаoxide is formed by the reаction of phosphorous (P4) with oxygen gas. P4 (s) + 3 O2 (g) --> P4O6 (s) If the reaction of 68.8 g of P4 with 18.8 g of O2 produces 21.0 g of P4O6, calculate the percent yield for the reaction.