b. David and Andrew are traveling to a Mathematics conference. David travels 110 miles in the same time that Andrew travels 140 miles. Andrew travels 15 miles per hour faster than David. Find the average rate of each person.

Step-by-step explanation:

Let x represent the speed of at which David travelled.

Andrew travels 15 miles per hour faster than David. It means that the speed of Andrew would be x + 15 mph

David travels 110 miles in the same time that Andrew travels 140 miles. The formula for time is expressed as

Time = distance/speed

Time taken for David to travel 110 miles is

110/x

Time taken for Andrew to travel 140 miles is

140 / (x + 15)

Since the time is the same, it means that

110/x = 140 / (x + 15)

Cross multiplying, it becomes

140x = 110 (x + 15)

140x = 110x + 1650

140x - 110x = 1650

30x = 1650

x = 1650/30

x = 55

David's average rate = 55mph

Andrew's average rate = 55 + 15 = 70 mph