Fluffy clouds XD - pressure n height

[vorcil]

Homework Statement

Puffy cumulus clouds, which are made of water droplets, occur at lower altitudes in the atmosphere. Wispy cirrus clouds, which are made of ice crystals, occur only at higher altitudes. On a typical day and at altitudes less than 11km
the temperature at an altitude y, can be given by T = To - Alpha*y
where To = 24.0 degrees celsius and Alpha = (6.00/1000m)

Find the altitude y(measured from sea level) above which only one cirrus clouds can occur

express your answer numberically in kilometers, using three significant figures.

Homework Equations

the ones above

The Attempt at a Solution

No idea really how to approach the problem
but i know it includes phase transition?
anyone care for a good ol explanation? XD cheers

 

[vorcil]

should i use the law of an ideal gas?

 

[vorcil]

Bah didn't read the question properly, it was bloody easy

it says the the cirrus clouds are made of ice crystals so i assumed the temperature was
0 degrees celsius

solving with the formula given i got 4000m or 4km high up is where cirrus clouds form