Answer:
a. Linear
A linear line is straight.
The quickest way to get the series is if you already know the series for sine:
Then just multiply the series by 
to get
The first four nonzero terms are simply the first four terms:
SP = 24
PQ/PT = PR/PS
7/14 = 12/x
1/2 = 12/x
x = 24
Think: (distance traveled by faster car) - (distance traveled by slower car) = 35 mi.
Using the formula distance = rate times time, we get for the faster car:
(55 mph)(t)
and for the slower car we get (50 mph)(t), so that
(55 mph)(t) - (50 mph)(t) = 35 mi. This can be simplified as follows:
(5 mph)(t) = 35 mi. Dividing both sides by 5 mph, we get t = (35 mi) / (5 mph).
Then t = 7 hours. The two cars will be 35 miles apart, going in the same direction, after 7 hours.
