Question 877535
Locus of points is the unknown (x, y).
The given line is x=16, so this is the variable point (16,y).  The other given point is (4,0).  


The description is that distance from (x,y) to (16,y) is two times the distance from (x,y) to (4,0).  Transpose this into an equation using the Distance Formula and simplify.