Ivy bought 10 packs of cups for her holiday party. A pack of MEDIUM cups costs $1.80 and a pack of LARGE cups costs $2.40. She paid a total of $21.60. How many packs of each size cup did she buy? First complete the equations below, where M stands for packs of Medium and L stands for packs of Large cups. [?]M+ [ ]L = 21.60; M + L = [ ]