Answer
a. $219.89$ grams
b. $310.17$ grams
c. $141.96$ grams
Work Step by Step
a. $P_4O_6$
Molar mass = $4*30.974+6*15.999=219.89$ grams
b. $Ca_3(PO_4)_2$
Molar mass = $3*40.078+2*30.974+8*15.999=310.17$ grams
c. $Na_2HPO_4$
Molar mass = $2*22.990+1*1.008+1*30.974+4*15.999=141.96$ grams