Scale = CD/ED
ED = 6º Ch.long. = 6 x 60 = 360nm at the Equator.
360nm = 667.3km = 667,300,000mm
Scale = CD/667,300,000 = 1/5,000,000
So:
CD = 667,300,000/5,000,000 = 667.3/5 = 133mm