The temperature of the earth's atmosphere drops about $5\backslash$deg C for every $1000$ m of elevation above the earth's surface. If the air temperature at ground level is $15\backslash$deg C and the pressure is $760$ mm Hg$,$ at what elevation is the pressure $380$ mm Hg$?$ Assume that the air behaves as an ideal gas.

The answer is z$=5550$m

Please explain with each value's unit.