Can anybody help with these questions?

What is the % Mg in MgO?

What is the % H in Ca(C2H3O2)2?

What is the % Ba in Ba(NO3)2?

What is the % of each element in Ni3(PO4)2?

What is the % of each element in Al2(CrO4)3?

What is the % of each element in (NH4)2(SO4)?