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: a person crosses a 800 m long street in 5 minutes. what is his speed in km per hour ?
Options: a. 1.23, b. 2.86, c. 4.36, d. 9.25, e. 9.61
[EX A]: e

[EX Q]: Problem: a cricketer whose bowling average is 12.4 runs per wicket takes 5 wickets for 26 runs and there by decreases his average by 0.4. the number age of the family now is :
Options: a. 18, b. 17, c. 76, d. 85, e. 86
[EX A]: d

[EX Q]: Problem: the length of a rectangle is increased by 40 % while its width is halved. what is the % change in area ?
Options: ['a. 25 %', 'b. 30 %', 'c. 50 %', 'd. 65 %', 'e. 70 %']
[EX A]:
b