A parallel-plate capacitor with plates of area S=100 cm^2 has a two-layer dielectric, as shown in figure below. Dielectric 1 is of thickness d1=1cm and has a relative permittivity of 3 and a dielectric strength five times that of air. The other layer (dielectric 2) is air, of thickness d2=0.5cm. Dielectric strength of air is 3 MV/m. What is the voltage across the whole capacitor that causes the breakdown? At breakdown, what is the voltage across the air layer only?