I think you mean what's the name of it,
they are called ordered points.
After one week it will be a total decrease of 175 milligrams
The way to get the equation for the radius (r) is to get r by itself. So divide each side by 4pi
500/4pi=r^2
Now take the square root of each side to get the equation of r.
sqrt(500/4pi)=r
