How many 3.8" X 7.7" pavers will it take to do an area that is 20' X 22' X 12' ?

If this is a tricky question, then the answer is simple, it can not be done.

Reason is 20' x 22' x 12' is not an area but volume. You will need to provide the thickness of the 3.8" x 7.7" pavers to cover volume area. So your info is missing.

If you are trying to cover surface area and duplicate sides are exactly equal, then it can be done as follows:

First you need to convert measurements to common denominator and that would be inches (easier to work with). After doing so you would multiply 44" x 91" and that would be 4004 squared inches.

Now if you are trying to cover surface area of 20' x 22' x 12' then we need to break that into parts. there will be 2 (20'x 22') plus 2 (20' x 12') plus 2 (22' x 12').

so now we have 126,720 + 69,120 + 76,032 = 271,872 squared inches.
take this number and divide it by 4,004 above number and that will give you 67.9 pavers, but you can not buy .9 of a paver, so you round it up and the answer is 68.

Hope that answers your question.