Problem: Gaston collected 64.50 in coins of 2 and 0.50. If he has four fewer 0.50 coins than three times the number of 2 coins, how many coins does he have of each denomination?
I think the first equation is: 2x + 0,5y = 64,50
x -> the amount of 2 coins
y -> the amount of 0,50 coins
But I don't know how to make the second one.