question

It is a mathematical EXPRESSION (NOT an equation), and as such , it can be ANY value.

 

IF you meant to ask : "What is  5x + 2 =0 ? " , then you have an EQUATION that can be solved thusly:

5x+2=0        Subtract 2 from both sides of the EQUATION

5x = -2         Divide both sides by 5

x = -2/5