Given there is a birdbath that holds 3 quarts.
We only want to fill it 3/4 of the way.
So, the number of quarts required to fill =

Now, we will convert from quarts to cups
As we know:
1 quart = 2 pints
and, 1 pint = 2 cups
So, 1 quart = 2 * 2 cups = 4 cups
So, we will convert from 9/4 quarts to cups as follows:

So, the answer will be:
It will take 9 cups to fill a birdbath