#1
I will draw the figure to see it and work on it
From the figure
Since CD // DE, then
From these conditions
Triangle ABC is similar to triangle AED
As a result of similarity, their corresponding sides are proportional

Since AB = 7, AE = 7 + x
Since AC = 5, AD = 5 + 3 = 8
Then

By using cross multiplication

Simplify it

Subtract 35 from both sides

Divide both sides by 5

Then the missing part x is 4.2