x(x+2)=55

Simplifying, we have  x^2 +2x - 55 = 0

I can tell this one is going to be "nasty."   Let's use the on-site calculator to solve.

$${{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,-\,}}{\mathtt{55}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = {\mathtt{\,-\,}}{\mathtt{2}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{14}}}}{\mathtt{\,-\,}}{\mathtt{1}}\\ {\mathtt{x}} = {\mathtt{2}}{\mathtt{\,\times\,}}{\sqrt{{\mathtt{14}}}}{\mathtt{\,-\,}}{\mathtt{1}}\\ \end{array} \right\} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = -{\mathtt{8.483\: \!314\: \!773\: \!547\: \!882\: \!8}}\\ {\mathtt{x}} = {\mathtt{6.483\: \!314\: \!773\: \!547\: \!882\: \!8}}\\ \end{array} \right\}$$

Anonymous was not technically incorrect. One answer was, indeed, around 6.5.

Since it's a quadratic, we'll also (usually) have a second different solution, as well.

it will be around 6.4 to 6.5