Labor Hour Totals On Estimates?

Thanks in advance to anyone who responds to this question...

We would like to be able to add up labor hours associated with line items on our estimates and extend on each line - then total hours for estimate. 

We have figured out how to create all of the custom fields within the estimate, but we are in the dark on how to make the calculations behind the scenes.

Is this relatively easy or difficult to do?

Example list of Columns:

ITEM:   DESCRIPTION:   QUANTITY:  PRICE:  EXT. PRICE:  LABOR:   EXT. LABOR

ESTIMATE DOLLAR TOTAL:   ESTIMATE LABOR TOTAL:

Thanks,

Richard