#1**+1 **

Triangle DBC is a 3-4-5 right triangle

So BC = 5

And AB = 20 - 5 = 15

So....since BDis parallel to AE.......we have this relationship

BC/ AB = CD/DE

5/15 = 4/DE

15/5 = DE /4

3 = DE/4 multiply both sides by 4

12 = DE

So

EC = ED + DC = 12 + 4 = 16

And by the Pythagorean Theorem,

AE = sqrt [ AC^2 - EC^2 ] = sqrt [ 20^2 - 16^2 ] = sqrt [ 400 - 144] = sqrt [ 256] = 16 ft

CPhill Dec 19, 2018