Dany bought a total of 20 game cards some of which cost $0.25 each and some of which cost $0.15 each

Dany bought a total of 20 game cards some of which cost $0.25 each and some of which cost $0.15 each

Dany bought a total of 20 game cards some of which cost $0.25 each and some of which cost $0.15 each. If Dany spent $4.2 to buy these cards, how many cards of each type did he buy?

Answer：12 cards at $0.25 and 8 cards at $0.15