Variable Overheads

 Kindly let me know how can we define and charge variable overheads in a process manufacturing inventory organization.

For example we have a plant resource 'MIXER1' and it has a resource cost of $10 for every 1 hour of use. Now i want that whenever this resource is run for 1 hour, a variable overhead cost of $1.5 is applied to this resource, so that the total cost of resource working for 1 hour should amount to $11.5 ($10 + $1.5).

Please let me know how can i do this.

Regards