Calculus problem (HELP)?

Many physical quantities are connected by inverse square laws, that is, by power functions of the form f(x)=kx^(-2). In particular, the illumination of an object by a light source is inversely proportional to the square of the distance from the source. Suppose that after dark you are in a room with just one lamp and you are trying to read a book. The light is too dim and so you move halfway to the lamp. How much brighter is the light?