Solve: 3(x - 2) = 21

First you look at BIDMAS, which determines the order in which functions are completed, [Brackets, Indices, Division, Multiplication, Addition, Subtraction], which says we deal with the brackets first, so we expand the bracket by multiplying everything in the bracket by whats outside it; in this case 3.

3x - 6 = 21

We then need to reaarange the equation to get x on its own, remember that when anything goes over to the other side of an equals sign it changes to the opposite of its function (positive - negative or multiply - divide). So the -6 goes across and becomes a positive 6:

3x = 21 + 6

3x = 27

Then the multiply by three goes over and becomes a divide:

x = 27/3

x = 9