A number is divisible by 8 , if the number formed by the last three digits is divisible by 8.
i.e 58N is divisible by 8 ⇒ N=4
Again a number is divisible by 11, if the difference between the sum of digits at even places and sum of digits at the odd places is either 0 or divisible by 11.
i.e, $(M+9+4+4+8) - (3+0+8+5+N) = M-N+9 = M+5$
It cannot be zero hence, $M+5 =11$ ⇒ M=6.