For example, if their log shows
Speed in miles per hour
Total elapsed time in hours
20
2
30
6
10
7
this means they drove 2 hours at 20 miles per hour, then 6-2=4
hours at 30 miles per hour, then 7-6=1 hour at 10 miles per hour.
The distance driven is then (2)(20) + (4)(30) + (1)(10) = 40 + 120
+ 10 = 170 miles. Note that the total elapsed time is always since
the beginning of the trip, not since the previous entry in their
log.
You will implement a function speed() that will help Bill and Ted compute the distance they traveled on several road trips. The input will come from file speed.txt and consists of one or more data sets where each data set represents a separate road trip. Each set starts with a line containing an integer n, 1 ≤ n ≤ 10, followed by n pairs of values, one pair per line. The first value in a pair, s, is the speed in miles per hour and the second value, t, is the total elapsed time. Both s and t are integers, 1 ≤ s ≤ 90 and 1 ≤ t ≤ 12. The values for t are always in strictly increasing order. A value of -1 for n signals the end of the input.
For each input set, output on the screen the distance driven, followed by a space, followed by the word "miles". The output for input file should be:Usage:
>>> speed()
170 miles
180 miles
90 miles