ROI Excel Help

[boomboomjr]

Can anyone help me with a formula in excel that would compare "my line" versus the "vegas line" and then spit out what the roi would be? I.E. I have the line at -180 and Vegas has -120 so if betting $100 roi would be 17.86%.

Right now I go to a website and plug it in...just thought it would be easier to have available in same program where my handicapping is done. Thanks in advance.