A bicyclist leaves from her home at 9 am and rides to a beach 40 mi away. Because of a breeze off the ocean, the temperature at the beach remains 60 °F throughout the day. At the cyclist's home the temperature increases linearly with time, going from 60 °F at 9 am to 80 °F by 1 pm. The temperature is assumed to vary linearly as a function of position between the cyclist's home and the beach. Determine the rate of change of temperature observed by the cyclist for the following conditions:
(a) as she pedals 10 mph through a town 10 mi from her home at 10 am;
(b) as she eats lunch at a rest stop 30 mi from her home at noon;
(c) as she arrives enthusiastically at the beach at 1 pm, pedling 20 mph.