I need help with the equation to solve the Percentage change in Net income for B4. I solved everything but this problem. Thank you!

The Parent Teacher Association (PTA) of Meadow High School is planning a fund-raising campaign. The PTA is considering the possibility of hiring Eric Logan, a world-renowned investment counselor, to address the public. Tickets would sell for $28 each. The school has agreed to let the PTA use Harville Auditorium at no cost. Mr. Logan is willing to accept one of two compensation arrangements. He will sign an agreement to receive a fixed fee of $10,000 regardless of the number of tickets sold. Alternatively, he will accept payment of $20 per ticket sold. In communities similar to that in which Meadow is located, Mr. Logan has drawn an audience of approximately 500 people. b-3. Assume the PTA pays Mr. Logan $20 per ticket sold. Determine the amount of net income that the PTA will earn if ticket sales are 10 percent higher than expected. Calculate the percentage change in net income. b-4. Assume the PTA pays Mr. Logan $20 per ticket sold. Determine the amount of net income that the PTA will earn if ticket sales are 10 percent lower than expected. Calculate the percentage change in net income. Complete this question by entering your answers in the tabs below. Assume the PTA pays Mr. Logan $20 per ticket sold. Determine the amount of net income that the PTA will earn if ticket sales are 10 percent higher than expected. Calculate the percentage change in net income. Complete this question by entering your answers in the tabs below. Assume the PTA pays Mr. Logan $20 per ticket sold. Determine the amount of net income that the PTA will earn if ticket sales are 10 percent lower than expected. Calculate the percentage change in net income