Answer:
550 pieces of candy (total), 150 pieces of candy for Maria, 200 pieces of candy for Lucas, 200 pieces of candy for Mateo.
Explanation:
Maria filled
6 + 4 + 5 = 15 boxes of candy.
Lucas filled
3 + 7 + 10 = 20 boxes of candy.
Mateo filled
3 + 7 + 10 = 20 boxes of candy.
x = 10 pieces of candy.
15x = 150 pieces of candy (Maria).
20x = 200 pieces of candy (Lucas).
20x = 200 pieces of candy (Mateo).
150 + 200 + 200 = 550 pieces of candy in total.