The slope is the change in y divided by the change in x.
The slope is the ratio of rise to run.
The slope is the rate of change of the function at a certain point.
The slope is the first derivative of a function.
Accordingly, the slope of this line
d=420-65t is the coefficient of variable "t" if we consider that d for the dependent variable and t for the independent
Therefore
slope = - 65
I hope you got the idea