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.

[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
[A]: b


[Q]: Problem: if the ratio of two number is 6: 7 and lcm of the number is 450 then what is the number.
Options: a. 11, b. 20, c. 25, d. 30, e. 35
[A]: a


[Q]: Problem: how many seconds will a 550 m long train take to cross a man walking with a speed of 3 km / hr in the direction of the moving train if the speed of the train is 63 km / hr ?
Options: a. 12 sec, b. 30 sec, c. 33 sec, d. 16 sec, e. 18 sec
[A]:
c