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 at 3 the solution is x=5
B. 562 both sides of the equation and then divide by 2 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