Answer: a) $10 per month b) the original runners
Step-by-step explanation: A) since runners cost $240, and you used them for a total of 2 years, which is 24 months. This means they cost 240/24 = $10 per month
b) The other pair costs $168 but you only have them for 2 months so they cost 168/2 = $84 per month which are more expensive.