Based on your comment I assume you want to find 7,533 subtracted by 7,200. To estimate this, round 7,533 to the hundreds place, so 7,533 becomes 7,500.
130=(1/3)(13)pix^2 times both sides by 3 390=13pix^2 divide both sides by 13 30=pix^2 divide both sides by pi 30/pi=x^2 sqrt both sides x≈3.09 radius is abou 3 units
