Margaret drove to a business appointment at $70 \mathrm{mph}$. Her average speed on the return trip was $60 \mathrm{mph}$. The return trip took $\frac{1}{3} \mathrm{hr}$ longer because of heavy traffic. How far did she travel to the appointinent?

Step 1 ：Margaret drove to a business appointment at a speed of 70 mph. Her average speed on the return trip was 60 mph. The return trip took 1/3 hour longer due to heavy traffic. We need to find out how far she traveled to the appointment.

Step 2 ：Since the distance traveled to the appointment and back is the same, we can use the formula for time, which is distance divided by speed, to set up an equation.

Step 3 ：The time for the trip there at 70 mph plus 1/3 hour equals the time for the trip back at 60 mph. We can write this as \(\frac{d}{70} + \frac{1}{3} = \frac{d}{60}\).

Step 4 ：Solving this equation for the distance, we find that \(d = 140\) miles.

Step 5 ：So, the distance Margaret traveled to the appointment is \(\boxed{140}\) miles.