We have to combine like terms in this expression. So, only -3 and -1 can be combined, and the same thing applies to 2x and -4x. If we add -3 and -1 as it says in the expression, that is -4. If we add 2x and -4x which is also in the expression, it is -2x. We can combine these two resulting terms to simplify the expression. The answer is -2x-4.
