Have a schedule with bookings blocked by colour

each block is 4hrs unless it is 6hrs (indicated with text 1800hrs)

have managed to get a total (say 8) of how many of each coloured block, but
want to have a final column that would tally hrs. i.e. if no 1800 then then
total (8) is multiplied by 4 = 32, but it could be (4*4) +(4*6)=40

Any chance?