Answer:
Shelly's average speed is 5.25 miles per hour.
It take 8 hours to travel 42 miles.
Explanation:
Given : Shelly biked 21 miles in 4 hours
To Calculate :
Shelly's average speed in miles per hour.
At that same rate how many hours will it take Shelly to bike 42 miles?
Solution :
We know that shelly traveled distance = 21 miles
She covered 21 miles in hours = 4
Now to calculate her speed we will use formula :
![Speed = (Distance)/(Time)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/ailgfscgsxg6gsnv86noa9ntzc9mum2vr0.png)
![Speed = (21)/(4)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/6fd2ccdow2qggav41sgz9z75iznbh4mg64.png)
![Speed =5.25](https://img.qammunity.org/2020/formulas/mathematics/middle-school/n0gcbf4gj6arct8eij8cnt6cwshlxybw0t.png)
So, Shelly's average speed is 5.25 miles per hour.
Now she traveled 42 miles with same speed (5.25 miles per hour)
Now time taken to cover 42 miles :
![5.25 = (42)/(Time)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/de52jz1upcx9oa1ba2x81e3pdfr0adxke0.png)
![Time= (42)/(5.25)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/rqzxfgakv2qbb7v3yc0jssi23ql91xepnx.png)
![Time= 8](https://img.qammunity.org/2020/formulas/mathematics/middle-school/k0czs0fphjejtb3kfqzrf7sfhdottamcpi.png)
Hence it take 8 hours to travel 42 miles.