You have t9 find a equal number
The general equation of a circle is
(x-a) ^ 2 + (y-b) ^ 2 = r ^ 2
for this case the values of a and b are
a = 2
b = 0
The radius of the circle is
r ^ 2 = 14
r = (14) ^ (1/2) = 3.74
First you find how much weight it lost
500 - 350 = 150
Then, to find the mean change you divide the weight lost by the number of months
150 : 6 = 25
25 is the monthly change