The illumination from a bulb varies directly as the intensity of the light and Intensity varies inversely as the square of the distance from the source. Two bulbs are placed 54 feet apart. The intensity, Ia, of bulb A is 64cd, and the intensity, Ib, of bulb B is 125cd. At how many feet from bulb A along the line between the two bulbs is the total illumination the least?

I have no idea how to start this problem...I thought about using optimization but I'm not sure where to start