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: the cross - section of a cannel is a trapezium in shape. if the cannel is 12 m wide at the top and 2 m wide at the bottom and the area of cross - section is 4200 sq m, the depth of cannel is ?
Options: a. 500, b. 600, c. 700, d. 800, e. 900
[EX A]: b

[EX Q]: Problem: two pipes a and b can fill a tank in 36 hours and 46 hours respectively. if both the pipes are opened simultaneously, how much time will be taken to fill the tank ?
Options: a. 20.195 hrs, b. 21.195 hrs, c. 22.195 hrs, d. 23.195 hrs, e. 20.495 hrs
[EX A]: a

[EX Q]: Problem: if - 3 x + 4 y = 28 and 3 x - 2 y = 8, what is the product of x and y ?
Options: a. 264., b. 428, c. 464., d. 622, e. 642
[EX A]:
a