#### Answer

Algebraic expression translation: $x - (x+4)$
Simplified form: $-4$

#### Work Step by Step

Let $x$ = the unknown number
The sum of the number and four:
$x+4$
A number decreased by the sum of the number and four:
$x - (x+4)$
Simplifying gives:
$=x-x-4
\\=0x-4
\\=-4$