How to add a fixed value to ANY cell in a chart based on a fixed condition

Hello

i am trying to make a chart to calculate how much $ I have on a daily commuter pass

This is a pass that gets daily deductions and then automatically reloads with a fixed amount
when the pass value drops below a set value

I.E. the card will reload with $30 when the value is <$20

is there a way for excel to automatically add 30 to ANY cell when the value of the cell is <20?

I attached a part of the workbook
the red cells are the ones I need to have 30 added to, and I want that to happen automatically

Thanks for your help