When acid X reacts with base Y to produce Mg3PO42- what are X and Y

Mg3(PO4)2 - Mg²⁺ forms basePO4³⁻ forms acidMa(OH)2 is a base(Y).H3PO4 is an acid(X).3Mg(OH)2 + 2H3PO4 ---> Mg3(PO4)2 + 3H2O