East Mullett Manufacturing earned operating income last year as shown in the following income statement:

Sales ................................................................$3,750,000
Cost of goods sold........................................... 2,250,000
Gross margin.................................................. $1,500,000
Selling and administrative expense.............. 1,200,000
Operating income............................................ $ 300,000
Less: Income taxes.............................. (@ 40%) 120,000
Net income....................................................... $ 180,000

At the beginning of the year, the value of operating assets was $1,600,000. At the end of the year, the value of operating assets was $1,400,000.

Required:
Calculate (1) average operating assets, (2) margin, (3) turnover, and (4) return on investment.