One thing you haven't said is that, in order for the length of NM to be 14, NM must bisect RS, RT, and RE. Further, each side of the triangles NME and NMR is half the length of a corresponding side of RST.
Use the idea that the triangles are similar. This will help you to find the solution. Also always find what part of another figure the object you need to find may be. In such a way you will find the necessary figure. I also always ask for help with math, usually at studydaddy service. It`s simple and you will get the necessary answer in any case.