If $(a,-20)$ is a point on the graph of $y=x^{2}+9 x$, what is $a$ ?

Step 1 ：Given that the point $(a,-20)$ lies on the graph of the equation $y=x^{2}+9 x$, we can substitute these values into the equation to solve for $a$.

Step 2 ：Substituting $x=a$ and $y=-20$ into the equation, we get $a^{2}+9a=-20$.

Step 3 ：Solving this equation, we find that the solutions are $a=-5$ and $a=-4$.

Step 4 ：These are the two possible values of $a$ for which the point $(a,-20)$ lies on the graph of $y=x^{2}+9 x$.

Step 5 ：Final Answer: \(\boxed{-5, -4}\)