Find an equation of the curve that satisfies
dydx=9(21y)\displaystyle {\frac{{{\left.{d}{y}\right.}}}{{{\left.{d}{x}\right.}}}}={9}{\left({21}-{y}\right)}
and y(0) = 6\displaystyle {6}.


y(x)=\displaystyle {y}{\left({x}\right)}=   .