How do you simplify $3x+5x+4$?

Hint: We separate the variables and the constants of the equation $3x+5x+4$. We apply the binary operation of addition for variables. The solutions of the variables and the constants will be added at the end to get the final answer.

Complete step by step solution:
The given equation $3x+5x+4$ is a linear equation of x. We need to simplify the equation by solving the variables and the constants separately.
All the terms in the equation of $3x+5x+4$ are either variable of x or a constant. We first separate the variables.
There are two such variables which are $3x$ and $5x$. The signs of the variables are both positive with coefficients being 3 and 5 respectively.
The binary operation between them is addition which gives us $3x+5x=8x$.
Now we take the constants. There is only one constant which is 4.

The final simplified form becomes $3x+5x+4=8x+4$.

Note: To more simplify the final solution we can also express it as the factor form.
We can take 4 as the common constant of the equation and get $8x+4=4\left( 2x+1 \right)$.
We can verify the result of the equation $3x+5x+4=8x+4$ by taking an arbitrary value of x as $x=2$.
Therefore, the left-hand side of the equation becomes
$3x+5x+4=3\times 2+5\times 2+4=6+10+4=20$
The right-hand side of the equation is $8x+4=8\times 2+4=16+4=20$.
Thus, verified the equation $3x+5x+4=8x+4$.