Popoy's is a snack house that recently opened near NU-Laguna, in its first week while selling milktea for 50 pesos per cup, Popoy's sold 750 pcs of burgers. A week later due to an increase in the price of sugar, Popoy's had to increse the price of its milktea to 55 pesos for that week 1000 pcs of burgers were sold. Solve for the cross-price elasticity of demand and tell whether milktea and burgers are seen by the customers of Popoy's as substitutes or complements.