A carnival charges $3 for kids and $10 for adults. On Saturday, there were 500 visitors, and the total amount taken at the gate was $3,600. The equation representing the number of visitors is k + a = 500, where k represents the number kids and a represents the number of adults. The equation representing the amount of money collected is 3k + 10a = 3,600. How many kids and adults visited the carnival?