Please solve this question with detailed explanation

20. Abbey Leisure Centre currently has 300 members. The centre's management board wants to expand the facilities. The board has decided to raise the cost of annual membership from the current price of $400. A survey has found that for each $20 increase in the annual fee, 10 members will not renew their membership. Prepare a report for the board of Abbey Leisure Centre, advising them of the cost of annual membership that will maximize the revenue