(3a, a) The problem states that the longer side of the rectangle is placed on the x-axis. Additionally, the problem states that the coordinate (0,0) is the bottom left vertex. That tells you that you don't have any translation going on, so you don't have to add a constant to either the X, or Y value. Finally, the problem states that the upper left vertex is at coordinate (0,a). Because of that and the fact that the lower left coordinate is at (0,0), the length of the shorter side of the rectangle has to be a. And three times the length of "a" is "3a". So the upper right coordinate has to have an X value of "3a" and a Y value of "a", or in other words (3a,a).