Given the task definition and input, reply with output. 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 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 %
a