The expression "3x + 2x" involves combining like terms, which are terms that have the same variable raised to the same power. In this case, both terms contain the variable x. To simplify the expression, you add the coefficients (the numbers in front of the variable) together. When you add the coefficients 3 and 2, you get 5. Therefore, "3x + 2x" simplifies to "5x." This means that if you have 3 of something represented by x and 2 more of the same thing, you now have a total of 5 of that thing, represented as 5x.