How do I simplify this algebraic expression 3x+2a-4x

Start by changing the -4x to + -4x.

So we have 3x + 2a + -4x.

To simplify, we can only combine what are called our like terms and in this problem, we have a pair of like terms in our x terms.

3x + -4x simplifies to -x.

So our answer is -x + 2a.

Note that if you wrote your answer as -1x + 2a, it means the same thing. However, as we move farther into math, we usually tend to drop the -1 or 1 that is in front of a variable since it's implied

0 is its x and y coordinate