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.

[EX Q]: 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
[EX A]: e

[EX Q]: Problem: a merchant marks his goods up by 30 % and then offers a discount of 10 % on the marked price. what % profit does the merchant make after the discount ?
Options: a. 17 %, b. 25 %, c. 69 %, d. 31 %, e. 19 %
[EX A]: a

[EX Q]: Problem: a lent rs. 5000 to b for 2 years and rs. 3000 to c for 4 years on simple interest at the same rate of interest and received rs. 1540 in all from both of them as interest. the rate of interest per annum is ?
Options: a. 7 %, b. 12 %, c. 74 %, d. 10 %, e. 45 %
[EX A]:
a