Answer: B.) 19.6 feet.
Draw a right triangle ABC. AB will represent the ladder, with point A being on the ground and point B being against the building.
Label: AC=6 ft, m<A=73° and <C is a right angle.
Use the trig mnemonic "SOHCAHTOA" to identify that BC/AC=tan<A. So BC, which is the height the ladder reaches, equals AC*tan<A=6*tan(73)=19.6 feet.
Explanation: