In mathematics, a percentage ("%") is a way of expressing a number as a fraction of 100 (per cent meaning "per hundred" in French).
Choose, if you would like to find A, B or X and insert the other two values!
$$X\% = \frac {A}{B} \times 100$$
B is X% bigger/smaller than A
$$X\% = \frac {B - A}{A} \times 100$$