What was Cowl’s rate of return on assets for 2007?

The following data pertain to Cowl, Inc. for the year ended December 31, 2007:

Net sales

$600,000

Net income

150,000

Total assets, January 1, 2007

2,000,000

Total assets, December 31, 2007

3,000,000

What was Cowl’s rate of return on assets for 2007?

a. 5%

b. 6%

c. 20%

d. 24%