Aspect ratio is SPAN divided by AVERAGE CHORD.
Wing span = 40.5 feet
Avg. chord = 6.3 feet
Aspect Ratio = 40.5 / 6.3
Aspect Ratio = 6.42
Keep in mind two airplanes can have very different wing span length but still have the same total wing area. An aircraft with a high aspect ratio generally produces less induced drag than low aspect ratio aircraft. Example: a glider (high aspect ratio) and a Piper Warrior (low aspect ratio).
High aspect ratio wings are more expensive to produce and are heavier.