Answer: a = 14.5 mm
Explanation: Perimeter is the measure of the outside, which to get you just add the outside values together. To find a, you take the perimeter that we know is 34.8 mm and subtract the 11.6 mm and 8.7 mm, which leaves us to have 14.5 mm. We can check that this value is approximately right because it is the hypotenuse, which is the longest side. Since the value is the biggest out of the other two, we can assume that we found the right value.