Hard to see this.....but....
AB = 50 BE = 20 DC = 35 CA = 54 DE = ????
Triangle ABE is similar to triangle DCE
So
BE / AB = EC / DC
20 / 50 = EC / 35
2 / 5 = EC / 35 multiply both sides by 35
( 2/5) * 35 = 14 = EC
And since
EC + EA = AC
14 + EA = 54
EA = 40
And AE / EB = DE /EC
40 / 20 = DE / 14
2 = DE /14 multiply both sides by 14
DE = 28