Find the slope of the line $3x+5y=20$.
We can find the slope and the $y$-coordinate of the $y$-intercept quickly by putting the equation in slope-intercept form.  Solving the equation $3x+5y=20$ for $y$ in terms of $x$ gives $y = -\frac{3}{5}x +4$.  So, the slope is $\boxed{-\frac{3}{5}}$.