[Question]: Chastity bought 4 lollipops which cost $1.50 each, and she also bought 2 packs of gummies which cost $2 each. If she has $15, how much was she left with after spending on the candies?
[Answer]: She spent 4 x $1.50 = $6 for the lollipops. She also spent 2 x $2 = $4 for the gummies. Therefore, Chastity was left with $15 - $10 = $5.
So the answer is 5.

[Question]: Martha has 18 crayons. She lost half of them, so she bought a new set of 20 crayons. How many crayons in total does Martha have after the purchase?
[Answer]: In the beginning, Martha lost 18 / 2 = 9 crayons. So after she bought a set of new crayons, she has in total 9 + 20 = 29 crayons.
So the answer is 29.

[Question]: Cary is an engineer in charge of designing an irrigation system for three farmers. Farmer Bob grows 3 acres of corn, 9 acres of cotton, and 12 acres of beans. Farmer Brenda grows 6 acres of corn, 7 acres of cotton, and 14 acres of beans. Farmer Bernie grows 2 acres of corn and 12 acres of cotton. If corn takes 20 gallons of water an acre, cotton takes 80 gallons of water an acre, and beans take twice as much water as corn, what percentage of the total water used will go to Farmer Bob's farm?
[Answer]:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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First figure out how much water beans take by multiplying the water use for corn by 2: 20 gallons / acre * 2 = 40 gallons / acre. Next, calculate Bob's water use by multiplying each plant's water use per acre by the number of acres he planted, then adding up the total water use for all three crops: 3 * 20 + 9 * 80 + 12 * 40 = 1260. Now do the same thing for Brenda: 6 * 20 + 7 * 80 + 14 * 40 = 1240. And do the same thing for Bernie: 2 * 20 + 12 * 80 = 1000. Now add up each farmer's water use to find the total water use: 1260 + 1240 + 1000 = 3500. Now divide Bob's water use by the total water use and multiply by 100 to find what percentage of the water he used: 1260 / 3500 * 100 = 36%.
So the answer is 36.