To solve the equation 2x + 4x = 21, start by combining like terms on the left side. Here, you have 2x and 4x, which can be added together:
2x + 4x = 6x
This simplifies our equation to:
6x = 21
Next, to isolate x, you need to divide both sides of the equation by 6:
x = 21 / 6
Now, simplify the fraction:
x = 3.5
Therefore, the solution to the equation is:
x = 3.5