Formula Field

Formula Field

I created a Reservation Database. I have Rate Column . So i want to auto update like this 
                          Company_Name=="aaa" Rate is 2500
                         Company_Name=="bbb" Rate is 1500
                          Company_Name=="ccc" Rate is 2000, so my report like this

Company Name Guest Name Check in       Check out Amount
aaa xxx       12-Jan-2014 14-Jan-2014       2500


Please help me.

Thank You.