Excel formula - Add days to date based on drop down selection

I want to add days to a date based on options selected from a drop down list. For example, if cell C5 reflects "New Hire" or "Post New Hire", I want cell C7 to add 90 days to the date in cell C6. But if "Extended New Hire" is reflected in cell C5, I want cell C7 to add 180 days to the date in cell C6. I am able to do


For one option, this formula works in cell C7:

=IF(C5="New Hire",$C$6+90)

I tried formula in cell C7 to adjust based on the text in cell C5, but it is returning a FALSE value instead:

=IF(OR(C5="New Hire",$C$6+90),IF(C5="Post New Hire",$C$6+90),IF(C5="Extended New Hire",$C$6+180))

Any ideas or help would be greatly appreciated :)