1.1. Define the following terms: differential cost, sunk cost, and opportunity cost? Give some illustrative examples? "Only variable costs can be differential costs" - Do you agree? Explain? 1.2. The number of X-rays taken and X-ray costs over the last six months in Imperial Hospital are given below: Month X-rays Taken X-ray Costs January 6,250 $24,500 February 7,000 $29.750 March 5,750 $22,500 April 6,500 $26,000 May 3,750 $18,000 June 5,500 $21,000 Required: a. Using the high-low method, estimate the cost formula X-ray costs? b. If 7,200 X-rays are taken in a month, should we use the cost formula above to expect X- ray costs? Why