Find the exact slope of the tangent line to the parametric curve {x=6cos(t)y=7sin(t)\displaystyle {\left\lbrace\begin{array}{c} {x}={6}{\cos{{\left({t}\right)}}}\\{y}={7}{\sin{{\left({t}\right)}}}\end{array}\right.} at the point where t=π3\displaystyle {t}=\frac{\pi}{{3}}.

Give an exact answer, do not use a decimal.