A number, x, decreased by the sum of 2x and 5 represent what equation

We set up this expression that we have to simplify. Although, to make it an equation, we set the expression given equal to the variable y, making this a function too.

y=x - (2x+5)

distribute the negative symbol

y=x-2x-5

combine like terms

y=-x-5

and that is our final answer