Is it common knowledge, or must it be documented?

It depends on what it is, because you didn't say what is common knowledge or documented.

JA is 9, AL is 10. Add them together and you get 19. CK is 14, so LK is 14. Add them together and you get 28. The other side of the triangle is the same as JA plus AL, 19. So to get the perimeter you add all the sides together: 
19+19+28=66
Your perimeter of your triangle is 66