Swifty Corporation recorded operating data for its shoe division for the year as follows:

Sales

$$600000$

Contribution margin

$150000$

Total fixed costs

$120000$

Average total operating assets

$400000$

What is the ROI for the year if management is able to identify a way to improve the contribution margin by $$40000,$ assuming fixed costs are held constant?

$15\%$

$17\%$

$8\%$

$18\%$