Correct answer is... 12 m. It is equal to 39 ft. Wingpan is calculated as stright line from one wingtip to another, so shape of the wing is not taken as factor during measurement. The biggest civil aircraft is 88 m (290 ft) wide, so Boeing Model 6D has 14% percent of it's length. Typical jet airliners are about 34 m wide, so in the comparision Boeing Model 6D has 14% of aircrafts like B737 or A320.
Disclaimer: Our articles and data connected to wingspan of Boeing Model 6D are based on public data from various sources. We are very picky to select an reliable data providers, but we cannot guarantee that everything is 100% error-proof. We recommend for any serious purpose - as a rule of thumb - to request offical data about wingspan from manufacturer of Boeing Model 6D.