If the mean of the following data is $5.5\text{, }$ then $x=$

$\begin{array}{r}{x}_i\\ \end{array}$	2	4	6	8
$f_i$	3	5	6	$x$

 

We have,  

   Mean= $5.5$

$\begin{array}{l}\Rightarrow \frac{6+20+36+8x}{3+5+6+x}=55\\ \Rightarrow 62+8x=(14+x)\times 5.5\Rightarrow 2.5x=15\Rightarrow x=6\end{array}$