Sum the time in hours/minutes based on selection in drop down list.

I need a formula that will sum the time in hours or minutes depending on the selection of the drop down list. For instance, in cell A, I have a drop down list, In cell B, I want to add the time spent on all items from the drop down list......that formula I have figured out, however in cell C, I want to add ONLY time spend. That formula is what I do not have. PLEASE HELP ME. I appreciate any effort to solve this.