1) You either expand, solve, factorise, simplify or some other
methods. Read the questions carefully.
2) With the answer you get, sub it back in to see if it satisfy the
original question and check your workings for careless
mistakes.
3) At secondary school level, ask yourself whether this is a linear
or quadratic question. If its quadratic, you usually bring
everything to one side and solve by X-factorisation method which
darknesshacker mentioned.
