Multiple variables in derivative and finding the slope

Multiple variables in derivative and finding the slope

I'm working on slope and geometrical differentiation. The problem is to
find the slope of any point on the curve $$\frac{x^2}{3^2} +
\frac{y^2}{2^2} = 1$$
I have found its derivative: $\frac{dy}{dx} = \frac{-4}{9} \frac{x}{y}$.
The next requirement is to give the numerical value of the slope at x = 1.
I obviously should give x the value of 1 in the derivative to calculate
but how should I approach dealing with the value of y? Thanks in advance.