During 2012, Martin Corporation sold merchandise costing $2,800,000 on an installment basis for $4,000,000. The cash receipts related to these sales were collected as follows: 2012, $1,600,000; 2013, $1,400,000; 2014, $1,000,000. What is the rate of gross profit on the installment sales made by Martin Corporation during 2012?

Select one:

a. 30%

b. 40%

c. 60%

d. 70%