Question

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

Answer 1

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

Answer 2

x- (2x+5)

I had that for homework too