Question 851997
x = length of each shortest side;
x+12 = another side;
-9+3x = the last side.


Perimeter, {{{2x+(x+12)+(3x-9)=117}}}
6x+3=117
6x=114
x=19


Knowing x allows you to compute the other two sides.




Note that a trapezoid has four sides.  This is why I showed "2x" immediately in the perimeter equation, skipping the separate, "x+x".