Step-by-step explanation: Say that the third side is y. The equation for the perimiter is side 1+ side 2+ side 3= perimeter which if you intput what we have turns out like (10x+2) +(8x-1)+y=24x-2. If you add 10x+2 and 8x-1 you get 18x+1. We can update the previous equation making it (18x+1)+y=24x-2. Since your trying to find y, you isloate it by subtracting (18x+1) from both sides. This leaves us with y=6x-3 as the length of thr missing side.
