The graphs of the equations $$y=k, \qquad y=\sqrt{3}x+2k, \qquad y=-\sqrt{3}x+2k,$$ are drawn in the coordinate plane for $$k=-10,-9,-8,\ldots,9,10.\,$$ These 63 lines cut part of the plane into equilateral triangles of side $$2/\sqrt{3}.\,$$ How many such triangles are formed?

(第十二届AIME1994 第6题)