|Sure, it's easy. Excel internally stores Dates and Times as numbers. Each day is a whole number and time is the decimal portion of that day. |
See here for a pretty good explanation of how Excel deals with Dates and Times as well as links to all the various Date and Time functions that Excel offers:
As for your question, simply subtract the number of Days required from the cell with the Goal Date.
With 11/01/2016 in A1, use this to return 9/20/2016:
(42 is 6*7, or 6 weeks.)
I'll leave the other two formulas to you. ;-)
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