Explain why circulation and rating systems determine how much money different advertisements cost to run.

This is really an economics question but they don't have economic as a choice of a category to select.

What is the state tax rate for a resident of arizona whose annual taxable income is $18,000?

Specialization—the division of labor—enhances productivity and efficiency by a) allowing workers to take advantage of existing differences in their abilities and skills. b) avoiding the time loss involved in shifting from one production task to another. c) allowing workers to develop skills by working on one, or a limited number, of tasks. d)all of the means identified in the other answers.

(a) what was the opportunity cost of non-gm food for many buyers before 2008? (b) why did they prefer the alternative? (c) what was the opportunity cost in 2008? (d) why did it change?