Which of the following describes the correct process for solving the equation 3x + 6 = 21 and arrives at the correct solution?
A. Divide both sides by 6 and then add 3. The solution is x = 5.
B. Add 6 to both sides of the equation and then divide by 3. The solution is x = 9.
C. Subtract 6 from both sides of the equation and then divide by 3. The solution is x = 8.
D. Subtract 6 from both sides of the equation and then divide by 3. The solution is x = 5.