Answer:
A. d = 5 − 15t; d = 18t
Explanation:
Derrick's distance from home is initially 5 miles and is decreasing at the rate of 15 miles per hour. His distance from home can be modeled by ...
... d = 5 - 15t . . . . . . d in miles; t in hours
Mark's distance from home is initially zero and is increasing at the rate of 18 miles per hour. His distance from home can be modeled by ...
... d = 18t . . . . . . . . . d in miles; t in hours
Together, these equations form the pair ...
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Comment on the equations
There is nothing in the problem statement or definition of the variables to suggest that one distance is measured in the same direction as the other, or that one value of d has any relationship to the other.
Usually, a "system of equations" expresses relationships among variables that all have the same definition with respect to some problem statement. Here, both values of d are "distance from home", but they don't necessarily have any relationship to each other. Their being the same value doesn't mean the boys have met, for example.