Write a system of equations to describe the situation below, solve using substitution, and fill in the blanks.
Nicholas went to play miniature golf on Monday, when it cost $6 to rent the club and ball, plus $4 per game. Lena went Thursday, paying $3 per game, plus rental fees of $15. By coincidence, they played the same number of games for the same total cost. How many games did each one play? How much did each one spend?
Nicholas and Lena each played __
games and spent $___
.