Analysis
The quickest (and cheapest) way to find the altitudes we want is to go out to NASA's web site and download a table. Using this table, we can look up the altitudes that correspond to pressures of 0.3 millibars and 11.5 millibars. Those altitudes are:
11.5 millibars ⇒ 30.125 km = 98,350 feet
0.3 millibars ⇒ 57.150 km = 187,500 feet