need help with these question

This problem refers to questions 8 and 9 The diagram below shows all the antinodal lines (solid) and nodal lines (dashed) due to two point sources tapping a water surface (the two dots in the middle of the circle are the two point sources). The sources are separated by an unknown distance d. The sources lie along a horizontal line. Are the two sources in phase or out of phase? Explain how you can tell from the diagram. If the two sources are out of phase, give the phase difference between the two sources. Explain. What is the source separation, d, in terms of the wavelength ? Explain your reasoning