First, you need to determine the scale factor. Divide one side in the larger triangle by the corresponding side in the smaller triangle. For example, 8/2. This would give you a scale factor of 2. Then you can reverse the process with the dimensions you need to get the area. The height of the larger triangle is 3.36, so to find the height of the smaller one, you divide it by 2, or the scale factor, to get the height of the smaller triangle which is 1.68. Next, you can solve for area of triangle using a=bh/2, so 4.2*1.68/2=a = 3.528.
