Patterning Question

I wasn't quite sure about this math question. I think that the answer is 10, because one side is5 cm, and the other side of the triangle is 41 mm. So I think that the answer is 10, or probably around 10. And if you add up all of the sides, they basicly add up to 16. I think that I may need some more help on these type of questions. I know all of the primeters in cm, and mostly all of the answers in mm as well. I know how to do the primeter basicly, but I think I need to learn a little bit more on how to use, and deal with the numbers in mm. I think this answer is 10 for the missing side of the triangle.