

I can’t. And you can’t. Real numbers are not provided. “you must trust the numbers given to you”
I can if I really want to. Down to the last receipt, excluding someones personal information and stuff like that, but in here all that data is public. Not in a sense that everything besides accounting and other “bigger picture” things would be online, but it’s public information anyways and it has to be accessible. Sure, I would definetly annoy the shit out of some poor secretary (or more likely multiple of them) digging up everything and it would take a long time, but it’s still public.
Delete windows partition with your preferred tool and
update-grub
should remove the item from boot menu. Then, depending on your partitioning schema, you can either create a new partition in the empty space and mount it however you like or expand your existing linux partition, but options there depend on how your partitioning has been originally built and if you can leverage things like LVM or ZFS when expanding the usable storage.And, while pretty obvious, make sure to only delete the correct partition and all data stored on that will be lost, so make sure you don’t have anything important on windows side of things.