CD = x
BC = y
AB = 85
BD = BC+CD = y+x
tan(angle) = opposite/adjacent
tan(28) = BC/AB
tan(28) = y/85
85*tan(28) = y
y = 85*tan(28)
y = 45.1953016912257
tan(angle) = opposite/adjacent
tan(31) = BD/AB
tan(31) = (y+x)/85
tan(31) = (45.1953016912257+x)/85
85*tan(31) = 45.1953016912257+x
51.0731526173427 = 45.1953016912257+x
51.0731526173427-45.1953016912257 = 45.1953016912257+x-45.1953016912257
5.877850926117 = x
x = 5.877850926117
So CD is roughly 5.877850926117 meters