Numbers: How to make a sum product of 2 columns numbers of which only those with checkboxes checked in a 3rd column respectively

EDIT (Complete revision):

Based on your data, the only way to accomplish this without redesigning the table is to create separate charts for each Segment shown. As each segment has 4 pieces of data, this is the only way to do this. (There may be someone out there who is a charting expert that could do much better, I'm sure)

First, as you have done is to make a Total chart:

Then crate separate charts, positioned together for the segments:

The charts can be edited for looks and data views in the Inspector but that is beyond the scope of the question.

In addition to njboot's answer, If you wish to drag and apply the ½ hour increments without entering a formula, be sure to select Both cells before dragging down the yellow dot. This will copy the pattern down (or across, for that matter.)

Edit:

If you want to use a formula:

Use Duration:

DURATION(weeks, days, hours, minutes, seconds, milliseconds)

Using Duration one can then adjust the increments later on affecting all cells with one simple change. For example, suppose you wish to change it to 15 minute increments or 2 hour or 25 minutes. This can be accomplished using a dynamic formula to allow for greater flexibility in your solution.

One could add a new table (or use hidden cells or whatever tickles one's fancy) to create an area where a number can be added that will change the increments universally.

Create Duration formula:

Notice that Hours and Minutes are tied to cells that can be adjusted without changing the formula.

Then, after dragging down the formula, just change the increments when desired.