$)$ Red light from a laser, $=650$ nm$,$ is incident on a double$-$slit. Successive fringes are $0\mathrm{.}32$ cm apart on a screen $2\mathrm{.}50$ m away. The diffraction pattern contains seven fringes in the central diffraction peak. What are the slit width and separation? Assume the first diffraction minimum occurs at an interference minimum.