Let’s call the number of seats in the stalls “4x” and the number of seats in the circle “3x”.

We know that the total capacity is 21,000, so:

4x + 3x = 21,000

Combining like terms:

7x = 21,000

Dividing both sides by 7:

x = 3,000

Now we can find the number of seats in the stalls:

4x = 4(3,000) = 12,000

And the number of seats in the circle:

3x = 3(3,000) = 9,000

Therefore, there are 12,000 seats available in the stalls and 9,000 seats available in the circle.