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: an optometrist charges $ 150 per pair for soft contact lenses and $ 85 per pair for hard contact lenses. last week she sold 5 more pairs of soft lenses than hard lenses. if her total sales for pairs of contact lenses last week were $ 1,220, what was the total number of pairs of contact lenses that she sold ?
Options: a. 9, b. 13, c. 15, d. 17, e. 19
[EX A]: a

[EX Q]: Problem: the average weight of 6 person ' s increases by 4.5 kg when a new person comes in place of one of them weighing 75 kg. what might be the weight of the new person ?
Options: a. 160 kg, b. 175 kg, c. 180 kg, d. 102 kg, e. 190 kg
[EX A]: d

[EX Q]: Problem: in what ratio mental a at rs. 68 per kg be mixed with another metal at rs. 96 per kg so that cost of alloy ( mixture. is rs. 80 per kg ?
Options: a. 5: 8, b. 4: 7, c. 4: 3, d. 9: 5, e. 9: 8
[EX A]:
c