A thin lens with a focal length of $+5\mathrm{.}0$ cm and an aperture $($full diameter$)$ of $6\mathrm{.}0$ cm has a $3\mathrm{.}60-$cm stop located $1\mathrm{.}60$ cm behind it $($the full diameter of the stop is $3\mathrm{.}6$ cm$).$ Locate the position and the size of the entrance pupil.