You set up a lemonade stand to raise money for your soccer tournament. You plan to sell cups of lemonade for $1.50/each. Your recipe calls for 8 lemons, 2 cups of sugar and 8 cups of water to yield 10 cups of lemonade.
You open your lemonade stand with 80 lemons, 3 bags of sugar containing 6 cups each, and 10 gallons of water (16 cups per gallon). What is the maximum you can make with the supplies on hand?
A) $112.50
B) $135
C) $75
D) $90

The requirements for the recipe are: 8 lemons, 2 cups of sugar and 8 cups of water to yield 10 cups of lemonade, so you must divide the total supplies into the requirements for the recipe and see how many glasses each reaches:

80 lemons / 8 lemons = 10 * 10 glasses of lemonade = 100 glasses.
3 bags of sugar * 6 cups = 18 cups of sugar / 2 cups of sugar = 9 * 10 glasses of lemonade = 90 glasses of lemonade.
10 gallons of water * 16 cups = 160 cups of water / 8 cups of water = 20 * 10 glasses of lemonade = 200 glasses of lemonade.

As you can see, although in water there are supplies for 200 glasses of lemonade or in lemons there are supplies for 100, sugar only allows 90 glasses of lemonade, so you must use this value to calculate the income from the sale of lemonade, the which, since it is worth $ 1.50 per glass you have:

Lemonade sales revenue = 90 * $ 1.50 = $ 135