Calculus optimization problem?

[achiu17]

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

 

[SteamKing]

If you were dealing with a single bulb, what would the illumination of say bulb A be at a distance x from the bulb?

Similarly, what would the illumination of bulb B be at a distance x?

Assuming that the illumination at a point between the two bulbs A and B is additive, how would you go about finding the point of least illumination?