how is this a tst problem
(a)
note that all of these must have every number that isn't the middle number equal, and thus our answer is $9\cdot10=\boxed{90}$ wow what an impossible tst problem
(b)
omg this is so so so much harder!1!!!!1!11!111!
anyways we do casework on if there are exactly $2021$ equal digits or not:
more than 2021:
This is $90,$ see (a).
exactly 2021:
more casework
the first digit is one of the 2021:
There are $1010$ ways to pick the number that isn't equal, $10$ ways to pick what this number is, $9$ ways to pick the equal digit, $90900$ total ways.
the first digit isn't one of the 2021:
There are $9$ ways to pick the first digit and $10$ ways to pick all other digits, $90$ total ways.
In total, there are $90900+90+90=\boxed{91080}$
watch me get this wrong