From the question, you have $10 to go bowling and you need to rent shoes for $4. Hence, after renting the shoes, you will have $10 - $4 left, that is you will have $6 left. To determine the number of games you can play, that will be the amount you have left after renting shoes divided by the cost of each game.
Multiples of 15 are: 15,30,45,60,75,90,105,120,135,150,165,180,195,210,225,240,255,270,285,300,315,330,345,360,375,390,405,420,435,450,465,480,495,510,525,540,555,570,585,600,615,630,645,660,675,690,705,720,735,