Final answer:
The slope of the line represented by the equation d=420-65t is -65, indicating the velocity of the car, which is 65 miles per hour towards its destination.
Step-by-step explanation:
The slope of a line represented by the equation d=420-65t can be interpreted as the rate of change of the dependent variable (in this case, distance) with respect to the independent variable (in this case, time).
In the equation, -65 is the coefficient of t, which represents the rate at which the car is approaching its destination or, in other words, the car's velocity. Hence, the slope of this line is -65, which indicates that the car is traveling at a speed of 65 miles per hour towards its destination.