Final answer:
Mr. Stein drove (140 - r) miles, where r represents the number of miles driven by Mr. Smith. This algebraic expression is subtracted from the total distance of 140 miles to the meeting.
Step-by-step explanation:
To determine how many miles Mr. Stein drove, we can use an algebraic expression. Since the total distance to the meeting is 140 miles and Mr. Smith drove the first r miles, we subtract the distance Mr. Smith drove from the total distance to find the distance Mr. Stein drove:
Total distance - Distance driven by Mr. Smith = Distance driven by Mr. Stein
140 miles - r miles = (140 - r) miles.
Therefore, the algebraic expression for the number of miles Mr. Stein drove is (140 - r) miles.