You and your brother each sell lemonade. You spend $35 on supplies and plan to charge $1.50 per cup. Your brother spends $20 on supplies and plans to charge $1per cup. How many cups of lemonade will each of you have to sell to earn the same amount of money?

Let's supposes the number of cups sold is c.

We can use an equation to solve this problem. Since both people are down some money, we will write the number they spent on supplies as negative, and use their rates as the unit rates for each side of the equation.

-35 + 1.50c = -20 + 1c
.05c = 15
c = 30

Thus, they will have to sell 30 cups.