How do I find the temperature of the air mass, and how do I use a t-skew chart?
I don't want to answer your question explicitly because it will ruin your education. Instead, I will guide you by asking three questions:

Where on the Skew-T are you?
Where on the Skew-T do you want to go?
What type of process do you want to undergo to get there? If it is dry and adiabatic, follow the dry adiabat ($\theta=T\left(\frac{P_0}{P}\right)^{\frac{R_d}{c_p}}$)

I recommend drawing the process out. Does the result make sense?