Please help me with part b of this question. Thank you in advance!!

Adecision is made at the margin when each alternative considers

In a market economy, supply and demand are important because theya. (i) play a critical role in the allocation of the economy's scarce resources.b. (ii) determine how much of each good gets produced.c. (iii) can be used to predict the impact on the economy of various events and policies.d. all of (i), (ii), and (iii) are correct.

"jake’s roof repair has provided the following data concerning its costs: fixed cost per month cost per repair-hour wages and salaries $ 20,900 $ 15.00 parts and supplies $ 7.70 equipment depreciation $ 2,800 $ 0.35 truck operating expenses $ 5,720 $ 1.60 rent $ 4,690 administrative expenses $ 3,850 $ 0.50 for example, wages and salaries should be $20,900 plus $15.00 per repair-hour. the company expected to work 2,600 repair-hours in may, but actually worked 2,500 repair-hours. the company expects its sales to be $47.00 per repair-hour. required: compute the company’s activity variances for may."