Please help solve!

In the figure below, two isotropic point sources of light (S, and S,) are separated by distance 2.62 um along a y axis and emit in phase at wavelength 900 nm and at the same amplitude. A light detector is located at point P at coordinate Xp on the x axis. What is the greatest value of Xp at which the detected light is minimum due to destructive interference? Answer in lambda