Answer:
12/13
Explanation:
It is because the 12 is over the 13, so you would you take A and B multiply by the 3 till you hit C. this will leave you with Z which is like the salt of the C but not like the buzz of the B. Once you memorized that you can understand that you must find cos(z) which you find by using a calculator or simply by pen and paper. Its a lot easier to just wright it down so you don't lose track of your numbers. scratch that, that had nothing to do with what I was talking about.
(ABC~XYZ means the two triangles are similar) If you look it is a dilation. (C maps to Z) so leg (BC maps to YZ) and (AC maps to XZ) XZ being the 13 and YZ being the 12.