1 A summary of 30 values of \(x\) gave the following information:
$$\Sigma ( x - c ) = 234 , \quad \Sigma ( x - c ) ^ { 2 } = 1957.5 ,$$
where \(c\) is a constant.
Find the standard deviation of these values of \(x\).
Given that the mean of these values is 86 , find the value of \(c\).