How does worst-fit memory allocation react when encountering contiguous empty memory blocks?
You have to assume that the blocks are what they are; if they can be coalesced into larger blocks, then this has already happened (ergo, perhaps the blocks that you have before you are not in fact adjacent in memory; they are an abstract list!) So, in short, there is no cumulative hole which spans multiple blocks.

So worst fit just walks the list of free blocks that it knows about and finds the largest block and takes from there.