Would like to keep updating single cell when conditions are met

E.g.  cell A19 has a value of 100.  cell A4 has a value of 10 with an adjacent B4 cell that will either have or not have a check mark.  I would like cell A19 to update to 90, IF B4 has a check mark. i would like this formula to be true to a range of values in the same columns continuously updating A19. So, if B5 has a checkmark, then A19 needs to subtracts value of A5.  etc etc etc.

I hope this makes sense. Thank you