A4.4 cm -thick layer of oil is sandwiched between a 1.2 cm -thick sheet of glass and a 2.9 cm -thick sheet of polystyrene plastic. how long (in ns) does it take light incident perpendicular to the glass to pass through this 8.5 cm -thick sandwich?

Along wire carrying a 4.2 a current perpendicular to the xy-plane intersects the x-axis at x=−1.7cm. a second, parallel wire carrying a 3.0 a current intersects the x-axis at x=+1.7cm. part a at what point on the x-axis is the magnetic field zero if the two currents are in the same direction? express your answer to two significant figures and include the appropriate units.