SumIF applied to a dynamic range

Hey all,

I hope to apply a SumIF function to a range defined by a few variables (lastRow, lastCol ect.). I prefer the result left in the cells as just the number, but getting the result by applying a formula in the cell will work as well. I have tried a few things, but couldn't make it work, so I really hope someone can help me out. Please see attached file, as it shows better what I need done. Thanks a lot in advance for you effort!
To make it easier I took most of the code out, leaving this:

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Thanks for the answer Andrew. The thing is that the formula depends on the parameters, which will change from time to time. Therefore, I need a formula where the ranges are given by the parameters. I tried something like the following, but had to give up cause I simply couldn't figure out how to do it.

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or

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