Why? 10 is the cover charge, since it's necessary I placed it alone. ( meaning multiply in math The 2 is the charge of each bingo card x, we don't know how many purchases are made so x will be right next to 2 meaning it's $2 per purchase. Since we don't know what x is we leave it as that. y is the cost in this equation, since we don't know what y is we just leave it as y.