The x-axis represents the trial, and the y-axis represents the number of defective lightbulbs.

For quality control, a company that manufactures lightbulbs conducted five different trials. In each trial, 500 different lightbulbs were tested. The bar graph above shows the number of defective lightbulbs found in each trial. The company wants the mean number of defective lightbulbs over six trials to be exactly 4.5. What must be the number of defective lightbulbs found in a sixth trial to achieve this target mean?