Since the line does cross the y-intercept at (0,0), our y intercept is 0. Next, from that point the closest point we are given is (2,1). Using the formula m = (y2-y1)/(x2-x1), we can find the slope.
m = (1-0)/(2-0) = 1/2. The slope is 1/2. Now make your equation:
y = 1/2x.
