To solve the equation follow these steps:
1. start by isolating the term containing the variable, -6x, on one side of the equation.
Subtract 3 from both sides:
-6x + 3 - 3 = 21 - 3
-6x = 18
2. Next, divide both sides of the equation by -6 to solve for x:
-6x/-6 = 18/-6
x = -3
Therefore, the solution to the equation is x = -3.