One of the formulas used to find the area of a triangle is:

Where A is the area, b is the base and h is the height of the triangle.
In our case, as we have a right triangle, one leg can be used as the base and the other can be used as the height of the triangle.
So, if the legs are 6 cm and 8 cm, we have that:

So the area of the metal brace is 24 cm^2, therefore the answer is A)