Background Paragraph: The Laffer curve depicts the amount of government revenue as a function of the rate of taxation. It shows that for a tax rate above a certain critical rate, government revenue starts decreasing as the tax rate rises, as a consequence of a decline in labour supply. This theory supports that, if the tax rate is above that critical point, a decrease in the tax rate should imply a rise in labour supply that in turn would lead to an increase in government revenue. 
Story: Bill is a tax agent, and is writing some tax law and is trying to decide the best rate. He knows that the average tax rate is 20% currently, but is unsure if he should push it above 30%, which is a higher than nominal rate and hasn't been tested. 
Question: Which tax rate would be more nominal for growth?
20%.