It clearly states that m and n are 2 digit numbers. You cannot include decimal numbers unless
otherwise stated

m-n=11x.

Statement 1
m=22,33,44,55..99 ;
22-11x=n
11(2-x)=n. Therefore x=1. Sufficient

Statement 2
m+n = 11k , where k is a positive integer
From the prompt m-n=11x

2m = 11(k+x). In order for m to be a 2 digit integer, x has to be an integer. Sufficient

when 2 digit number is mentioned, it means without decimal...
A) m=99, n=11 true and if n=12, not true. insufficient
B) m+n is multiple of 11. m=12 and n=21 not true, m=11 and n=11, true.
Insufficient
A&B) m is multiple of 11 and m+n also. thus n is also multiple of 11. or m-n is also
IMO C