Answer : 25t + 45m represent the length that the car travels
In this case, the car is traveling at 2 different velocities, 25miles/hour then 45 miles/hour. The 25 and 45 represent those two velocities.
The car is also driving in different duration, t hours at 25mi/h and m hours for 45mi/h. The t hours and m hours is represent the duration.
If you multiply duration and velocity, you will get the distance the car go.