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: 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
b

Problem: what is the smallest number by which 2880 must be divided in order to make it into a perfect square ?
Options: a. 3, b. 4, c. 5, d. 6, e. 7
c

Problem: the average price of an decoration piece increases over the years. if from 1990 to 1996, the price of the decoration piece increased by 13 % and from 1996 to 2001 it increased by 20 %, what is the price of the decoration piece in 2001 if the price in 1990 was $ 11500 ?
Options: a. $ 15594., b. $ 15322., c. $ 14786., d. $ 14543., e. $ 12988.

a