math
posted by nancy .
Mr. Mitchells office is on a winding side road next to a highway exit.He is driving on the highway at 60mph, and at this rate he expected to arrive at his office at 8:45a.m.However at 8:30 he was forced to leave the highway and take the side road, driving at a steady speed of 40 mph for the rest of the way, he arrived at his office 15 min. later than originally planned
How many miles did he drive on the side road?
show your work and explain your answer!

At 60 mph, he was going 1 mile a minute. So, Mitchell had 15 miles to go if he'd stayed on the highway.
At 40 mph, he would go 20 miles in 1/2 hour.