Hopefully you have now realised that something based around opening hours might be more reasonable. This time we get:
Agents(80%, 30, 20,000 / 80, 330) x 80
That is, the number of agents required in a typical hour multiplied by the number of opening hours.
This time the answer is 2,240, exactly the same as the first calculation. With a bit of thought, it soon becomes clear why the two calculations are arithmetically the same.