Answer:
x = 6
Explanation:
3x + 3 = 21
It is simple, linear equation which involves only one variable for which we need to solve it.
To solve this, just take all the constants to one side of the equation, keeping in mind to change their signs if you move them across the '=' sign, and keep the variable on the other side:
3x + 3 = 21
3x = 21 - 3
3x = 18
Now divide the constant number with the coefficient of x to get the answer:
x = 18 / 3
x = 6