Please HELLLLP?????, Earth Science Question. I cannot figure THIS OUT!?

[Livefor2day]

CHANGING TEMPERATURE WITH HEIGHT:

SPRING DAY: OK
Amiddle latitude city 40* N lattitude
HAS A SURFACE (SEA LEVEL) TEMP. OF 15* C
If a vertical sounding reveals a nearly constant lapse rate of 6.5*C Per KILOMETER AND A TEMPERATURE AT THE TROPOPAUSE OF _-60*C, wHAT IS THE HEIGHT of the tropopause?????

and they ask to show calculations , to the nearest tenth of a kilometer

Please this is buggin me, its not even my homework but I cannot figure it out

[Monty Burns]

Ok. You would find the difference between the temp of the tropopause and the surface temp. So it'd be 75. The you divide the 75 by 6.5 and it comes out to be 11.5 km (11,500m) or 7.2mi. (38076.9ft.)