10. It is 21,000 kilometers around the earth and the earth rotates in 24 hrs. How fast is it rotating

Speed is measured in miles per hour (mph).

The formula Distance equals rate times time (d=rt) can be rearranged and the rate can be solved,

d = r*t = > r = d / t. d = 100 miles, time = 6 hours, Rate = 16.66 mph (16 and two thirds).

The same formula can be used for the second part,

21000 / 24 = rate, Rate = 875 kilometers per hour