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 area of a square field is 625 km 2. how long will it take for a horse to run around at the speed of 25 km / h ?
Options: a. 12 h, b. 10 h, c. 8 h, d. 4 h, e. none of these

A: d
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Q: Problem: if a = 105 and a ^ 3 = 21 × 25 × 45 × z, what is the value of z ?
Options: a. 35, b. 42, c. 45, d. 49, e. 54

A: d
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Q: Problem: if rs. 7500 are borrowed at c. i at the rate of 4 % per annum, then after 1 year the amount to be paid is ?
Options: a. 3377, b. 2688, c. 2688, d. 7800, e. 1268

A:
d
****