I'm unsure of the correct notation here so please bear with me.
Provided that x is a positive integer:
will produce a number which is 1 followed by n-1 0's. What I mean is that:
, which is 1 followed by
0's
which is 1 followed by
0's
will be a 1 followed by 29 zero digits.
If x is greater than one, as it is in your case, and an integer, it will end in 10 and be preceeded by (x-2) nines.
Eg:
x-2 = 4
The result is four 9's followed by 10.
x=9
x-2=7
There are 7 nines followed by 10.
So in your example:
10^30-90
x=30
You will have 28 nine's followed by a 10.
The sum of the digits will be:
which is, as you say, 253