We have the formula for the area of a triangle equal to A=l*w, where stands for the area, l for the length and w for the width. Given in the problem are the following:
A=135 m
l=6+w
w=w
Solving for the value of w, we have:
A=(w+6)*w
135=w²+6w
w=9 meters
Therefore, the length of the rectangle is 15 meters.