The method I was taught back in school:

SOHCATOA can only be used for right-angles, so split the triangle in half to get two 90 degree angles.

Then use TOA to get the answer. Tan(70)=6/x, with 6 being the line opposite the numbered angle, and the unknown side being the adjacent one.

Plug that into a calculator and end up with 2.18382... Now multiply that by 2 (for the complete triangle, not the chopped in half one), and get

4.368