Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Problem: a bottle contains a certain solution. in the bottled solution, the ratio of water to soap is 3: 4, and the ratio of soap to salt is five times this ratio. the solution is poured into an open container, and after some time, the ratio of water to soap in the open container is halved by water evaporation. at that time, what is the ratio of water to salt in the solution ?
Options: a. 9: 32, b. 9: 30, c. 32: 9, d. 19: 32, e. 18: 30
a

Problem: what is the sum of natural numbers between 30 and 100
Options: a. 4615, b. 4860, c. 5000, d. 5500, e. 5550
a

Problem: the milk level in a rectangular box measuring 58 feet by 25 feet is to be lowered by 6 inches. how many gallons of milk must be removed ? ( 1 cu ft = 7.5 gallons )
Options: a. 100, b. 250, c. 750, d. 5437.5, e. 5635.5
d