In a double slit experiment the separation among the slits is 0.15mm, the distance between the slits and the screen is 140 cm, the wavelength of the light utilized is 643 nm. (a) What is the path difference among rays at a point 1.8 cm from the central maximum on the screen? (b) What is the phase difference among rays at this point? (c) Is this a point of maximum, minimum, or intermediate intensity of light in the interference pattern?