1. x[n] is a real and even signal
2. x[n] has period N = 10 and Fourier coefficients $ \ a_k $
3. $ \ a_{11} = 5 $
4. $ \ \frac{1}{10} \sum_{n=0}^{9}|x[n]|^2 = 50 $
From #2 gives the period of N=10, from that can deduce that the frequency w = k\frac{2\pi}{10} and if assume k=1 then the frequency w=\frac{\pi}{5}
