Answer:
![A.\ r = \frac{d}{t}](https://tex.z-dn.net/?f=A.%5C%20r%20%3D%20%5Cfrac%7Bd%7D%7Bt%7D)
![B.\ r = 200,000m/h](https://tex.z-dn.net/?f=B.%5C%20r%20%3D%20200%2C000m%2Fh)
![C.\ r = 200\ km/h](https://tex.z-dn.net/?f=C.%5C%20r%20%3D%20200%5C%20km%2Fh)
D. Kilometres makes more sense
Step-by-step explanation:
Given
d = rt
d = 800,000 metres
t = 4 hours
Required
Answer Part A to D
A. Rearrange the formula;
Here, we simply divide both sides by t
![d = rt](https://tex.z-dn.net/?f=d%20%3D%20rt)
![\frac{d}{t} = \frac{rt}{t}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bt%7D%20%3D%20%5Cfrac%7Brt%7D%7Bt%7D)
![\frac{d}{t} = r](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bt%7D%20%3D%20r)
Reorder
![r = \frac{d}{t}](https://tex.z-dn.net/?f=r%20%3D%20%5Cfrac%7Bd%7D%7Bt%7D)
B. Solve for r in metres per hour
Here, d = 800,000 metres and t = 4 hours
becomes
![r = \frac{800,000m}{4h}](https://tex.z-dn.net/?f=r%20%3D%20%5Cfrac%7B800%2C000m%7D%7B4h%7D)
![r = 200,000m/h](https://tex.z-dn.net/?f=r%20%3D%20200%2C000m%2Fh)
C. Solve for r in kilometre per hous
We start by converting d = 800,000 metres to kilometres
If
, then
![800,000 metres = 800,000 * 0.01 kilometre](https://tex.z-dn.net/?f=800%2C000%20metres%20%3D%20800%2C000%20%2A%200.01%20kilometre)
![800,000 metres = 800 kilometre](https://tex.z-dn.net/?f=800%2C000%20metres%20%3D%20800%20kilometre)
So,
and ![h = 4 hours](https://tex.z-dn.net/?f=h%20%3D%204%20hours)
becomes
![r = 200\ km/h](https://tex.z-dn.net/?f=r%20%3D%20200%5C%20km%2Fh)
D. Which unit makes more sense
As a standard, when calculating speed or velocity, metres is used viz a viz seconds while kilometres is used along with hours;
Since, the first unit (metres) is best used with seconds and the second unit (kilometre) is best used with hours, it's safe to conclude that kilometres makes more sense