Write the molecular, ionic, and net ionic equation of
a) MgCl2(aq) + K3PO4(aq)--->


b) Na2CO3(aq) + HBr(aq)--->

You have to check the solubility of all the compounds present in the solution
molecular equation
3MgCl2(aq) + 2K3PO4(aq)--->6KCl (aq) + Mg3(PO4)2(s)
complete ionic equation
write all aq in complete ionic  form
3Mg2+ (aq) + 6Cl-(aq) +  6K+(aq)  + 2PO4 3- ----> 6K+(aq) + 6Cl-(aq) + Mg3(PO4)2(s)
now cancel the spectator ions or the ions which are present on both the sides of the equation to get the net ionic equation
follow exactly same method for the remaining