Use the std eqn of a circle with center at (h,k) and radius r:
(x-0)^2 + (y+2)^2 = 9^2, or just x^2 + (y+2)^2 = 9^2.
6 is the answerI equations
Answer:

Step-by-step explanation:
Proportion of Heat Loss Between sundown and midnight
Proportion of Heat Loss between midnight and 4 AM 
Proportion of Total Heat Already Lost 
Proportion of Remaining Heat 
Between 4 AM and 5 AM, five-eighths of the remaining heat is lost.
Proportion of Heat Loss between 4 AM and 5 AM= 
Therefore, Proportion of Remaining Heat Left 
We therefore say that:

Adam: 15 miles / 3 = 5Mi/Hr
Ben: 12 miles / 2 = 6Mi/Hr
Hope this helps!