The perimeter is 10.3. I think that's already in significant digits, but I'm not sure. We just got finished learning that in chemistry and it confused me to death!
Linear angles are two angles that are part of a straight angle (180*), so both must add up to 180. If 4x+3+10x-5+180, then 14x-2=180, then 14x=182, and x=13