Formula Function for a specific Picklist

Formula Function for a specific Picklist

I am using a picklist field which is 'committed time line' which has values (1,2,3,4,5,6,7,8) weeks. What I want is , if a person selects '1' then the formula should return current date + 1 week and so on. I am unable to use the formula effectively.
 Need your help to the soonest .
Thanks.