MATH GRADE 10****
posted by alyssa .
Scott, Arif, and Diane run a small delivery company. For thier business, they use licensed twoway radios with a 20 km range. Scott is at their office which they have marked as the origin on their map of the town. Arif is dropping off a package at (8, 16) while Diane is making a pick up at )4,20)
a) Find an equation that desrcibes the boundry of this area

If "the area" is a triangle, it would take three equations to define the boundary. I don't see what the 20 km range of the radios has to do with that boundary.
If what they want is the equation of the boundary of radio reception, it is the circle
x^2 + y^2 = 20^2 = 400
Diane is outside the boundary and Arif is inside it. 
does anybody knows how to solve for x+2y is