Answer:
Plot the given points on a piece of graph paper. You should find three points that are the corners of a square. It's then pretty easy to see where the missing point would go. (This works even if you just sketch your own x and y axes with tick marks that are kinda equally spaced.) The missing corner B is at (8,7).
Since the center of dilation is at the origin, and it's dilated by a factor of two, each of the coordinates are moved to twice their original distance from the origin.
B(8,7) becomes B'(16,14).