an architect notices that the scale on a blueprint he is using has been torn off. however, he sees that a 21.6-foot wall that has been built is 6 inches long on the blueprint. what is the scale for this blueprint?

a. 1 in. : 3.6 ft.
b. 1 in. : 6.3 ft.
c. 1 in. : 36 ft.
d. 1 in. : 63 ft.