1. The problem statement, all variables and given/known data A 5.9cm-thick layer of oil (n=1.46) is sandwiched between a 1.3cm -thick sheet of glass and a 2.4cm-thick sheet of polystyrene plastic (n=1.59) How long (in ns) does it take light incident perpendicular to the glass to pass through this 9.6cm -thick sandwich? 2. Relevant equations n=c/v v=fλ 3. The attempt at a solution I am very confused to this problem because I am unsure of how to incorporate the length of the different mediums into the equations.