Find the value of k\displaystyle {k} for which the constant function x(t)=k\displaystyle {x}{\left({t}\right)}={k} is a solution of the differential equation

6t5dxdt6x9=0\displaystyle {6}{t}^{{5}}\frac{{{\left.{d}{x}\right.}}}{{{\left.{d}{t}\right.}}}-{6}{x}-{9}={0}.