Final answer:
The expression 4x + 8x is simplified by combining like terms and adding the coefficients, which results in 12x.
Step-by-step explanation:
To simplify 4x + 8x using the properties of operations, we can use the combine like terms property which states that we can add or subtract coefficients of like terms.
In this case, both terms have the variable x and therefore can be combined.
We simply add the coefficients of x: 4 and 8, which gives us 12x. So, 4x + 8x simplifies to 12x.