We know that tan ∅=opposite side angle ∅/adjacent side angle ∅ adjacent side angle ∅=opposite side angle/tan ∅
in this problem see the attached figure to better understand the problem angle ∅=80° opposite side angle ∅=12 ft (AB) adjacent side angle ∅=? (AC) adjacent side angle ∅=12/tan 80°------> 2.12 ft