Hi Sharvari
What Pavan is explained is from actual FI entries your actual cost will be booked for labour cost..but in your case this is an agreement labour cost @150/- per hr. If you follow Actual activity calculation as Pavan told may vary from your rate of 150/- based FI entries and actual activity consumed in various orders...In my opinion it will nor work.
You may consider costing sheet Qty based rate where you can define 150/ per unit cost based on actual activity..
kamal