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: if a lends rs. 3150 to b at 8 % per annum and b lends the same sum to c at 12.5 % per annum then the gain of b in a period of 2 years is ?
Options: a. 280, b. 295, c. 283.5, d. 245, e. 200
c

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: joe needs to paint all the airplane hangars at the airport, so he buys 360 gallons of paint to do the job. during the first week, he uses 1 / 4 of all the paint. during the second week, he uses 1 / 2 of the remaining paint. how many gallons of paint has joe used ?
Options: a. 18, b. 225, c. 175, d. 216, e. 250

b