A summary of 40 values of \(x\) gives the following information:

\(\Sigma(x-k) = 520\), \(\Sigma(x-k)^2 = 9640\),

where \(k\) is a constant.

(a) Given that the mean of these 40 values of \(x\) is 34, find the value of \(k\).

(b) Find the variance of these 40 values of \(x\).