Answer:
7 seconds
Explanation:
In 1 second, the distance covered by the car is 3 feet.
We know that:
[tex]\text{Average Speed=}\frac{\text{Distance}}{\text{Time}}[/tex]Therefore, the average speed of the car will be:
[tex]S\text{peed}=\frac{3}{1}=3\text{ ft per second}[/tex]We want to determine the time when:
Distance = 21 feet
Substitution into the formula for average speed gives us:
[tex]\begin{gathered} 3\text{ ft per second = }\frac{21}{\text{Time}} \\ 3\times\text{Time}=21 \\ \text{Divide both sides by 3} \\ \text{Time = 7 seconds} \end{gathered}[/tex]Therefore, it takes 7 seconds to drive 21 feet.
