How do I calculate how much my job’s pre-tax lunch was for the whole year WITHOUT having to calculate my total wages for the year?

The pre-tax lunch (as an earning which was also deducted; I am exempt from “FICA” and “State” for this benefit) was so far deducted from approximately 16 of my paychecks for the year. I have calculated how much per day I spent on the lunch BEFORE taxes, but I need to know how to calculate the AFTER-TAXES total.
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