Ais a service that people need but are usually unable to provide for themselves.

The answer to fill the blank space is "Public Good".
Complete sentence will be:
Public good is a service that people need but are usually unable to provide for themselves. It refers to any kind of service which usually is provided without the profit or loss values for each and every member of that society. The service is provided by government or some organization.

a progressive tax is a tax that imposes a lower tax rate on low-income earners compared to those with a higher income, making it based on the taxpayer's ability to pay. that means it takes a bigger percentage from high income earners than it does from low income people.

answer; someone must cover the cost associated with the provision of scarce goods in both sectors;