If W stands for wages/salaries, P for profits, R for interest and Z for rent on land and real estate, then national income is

If W stands for wages/salaries, P for profits, R for interest, and Z for rent on land and real estate, then the national income is given by:

W + P + R + Z

This is because national income is the total amount of income earned by individuals and firms within a country's borders, and it includes all four components of W, P, R, and Z.

Wages and salaries are earned by employees, profits are earned by business owners, interest is earned by lenders, and rent is earned by landlords. When we add up all of these components, we get the total national income.

Therefore, "W+P+R+Z," is the correct answer.