#### Answer

2 $\times$ ( 8 + x ) = x - 20

#### Work Step by Step

Problem: Twice the sum of 8 and a number is the difference of
the number and 20
Let's start from the beginning.
Twice the sum means we should have 2 $\times$ ( some sum )
The sum = 8 and a number
Let's call the number x so the sum = 8 + x
Now, we have 2 $\times$ ( 8 + x )
"is" means =
the difference of the number and 20 means we should subtract 20 from x
so 2 $\times$ ( 8 + x ) = x - 20