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: a person purchases 90 clocks and sells 40 clocks at a gain of 10 % and 50 clocks at a gain of 20 %. if he sold all of them at a uniform profit of 15 %, then he would have got rs. 40 less. the cost price of each clock is :
Options: a. 50, b. 90, c. 80, d. 28, e. 93
c

Problem: in n is a positive integer less than 200, and 14 n / 60 is an integer, then n has how many different positive prime factors s ?
Options: a. 2, b. 3, c. 5, d. 6, e. 8
b

Problem: how many seconds will a train 100 meters long take to cross a bridge 140 meters long if the speed of the train is 36 kmph ?
Options: a. 26, b. 24, c. 25, d. 82, e. 27

b