Hi there! The third option shows us the best setup.
We can find the area of a triangle with the standard formula area = 1/2 * base * height.
To be able to fill in this formula, we need to have a base and a height. We can't easily find a triangle with given base and height, so we must look for another option.
We can also take the area of a square (length × width) and then divide the answer by 2. This is possible when we take the third setup. Hence the third answer is correct.