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: x does a work in 20 days. y does the same work in 40 days. in how many days they together will do the same work ?
Options: a. 10, b. 12, c. 20, d. 30, e. 13.33
e

Problem: find the curved surface area, if the radius of a cone is 35 m and slant height is 30 m ?
Options: a. 1100, b. 2200, c. 3300, d. 4400, e. 5500
c

Problem: in a group of 100 cars, 49 cars do not have air conditioning. if at least 51 cars have racing stripes, what is the greatest number of cars that could have air conditioning but not racing stripes ?
Options: a. 49, b. 47, c. 48, d. 51, e. 53
a