Any point that is co planar with one another and is also equidistant from a given point is a circle. We need it to be co planar, otherwise it would be 3-dimensional and create a sphere. And if they we not all equidistant, they would not make an even circle (it'd be an oval or another shape).
This would bring you to $160.00. This is because you initially had $20.00, because of the $13 and $7. Then, your family gave you a total of $140.00, and 140 + 20 = 160.
