Solve 3(x-2)=21

This question can be solved in two ways. One way is to divide the whole equation, both sides by 3, which gives x-2=7. Then add 2 to both sides to give x=9. Another way is to work out the left hand side of the equation first, which gives 3x-6=21. Then add 6 to both sides to give 3x=27. x can then be worked out by 27/3=9.