If you put this formula in cell D3, would that do the trick?
Formula:
=SUMPRODUCT(INDIRECT(ADDRESS($D$2+4,1)&":"&ADDRESS($E$2+4,1)),INDIRECT(ADDRESS($D$2+4,2)&":"&ADDRESS($E$2+4,2)))/SUM(INDIRECT(ADDRESS($D$2+4,1)&":"&ADDRESS($E$2+4,1)))
The Address-function uses the values in D2 and E2, but need to add 4 to it to get the right row. You could make this more flexible by naming the ranges used in the sumproduct-function and referring to its top row with ROW(myRange). Same can be done with the column number.
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