Final answer:
Equations a), c), and d) cannot be used to find the travel time for a car traveling at a constant rate of 70 miles per hour because they do not correctly apply the distance-speed-time relationship with the given speed.
Step-by-step explanation:
To determine which equation cannot be used to find the travel time for a car traveling at a constant rate of 70 miles per hour, we need to consider the distance-speed-time relationship given by:
Distance = Speed × Time or d = s × t.
Let's analyze each equation:
a) 20 = 7t - This cannot be correct as 7 does not correlate to the speed of 70 mph.
b) 200 = 70t - This is correct as it represents the equation d = s × t, where d=200 and s=70.
c) 15 = 5t - This is not applicable to our current scenario because the speed is not given as 70 mph.
d) 100 = 50t - This also does not relate to our scenario of traveling at 70 mph.
Therefore, the equations a) and c) and d) cannot be used to find the travel time at 70 mph, but equation b) can.