Answer is: AX + BY → AY + BX.
For example, balanced chemical reaction:
3K₂SO₄(aq) + Ca₃(PO₄)₂(s) → 2K₃PO₄(aq) + 3CaSO₄(s).
This chemical reaction is double displacement reaction - cations and anions of the two reactants switch places and form two new compounds.
aq(aqueous) means dissolved in water.
s(solid) means that salt not dissolved in water.