4. A netizen's $QQ$ number is $m, m$ when divided by 10000, the sum of the quotient and the remainder is $18889, m$ when divided by 100000, the sum of the quotient and the remainder is 58741. Then the hundred's digit of $m$ is $(\quad$.
(A) 4
(B) 5
(C) 6
(D) 7
4.C.

Let the remainder when $m$ is divided by 10000 be $a$, and the quotient when divided by 10 be $b$, with the remainder being $c$. According to the problem, we have
$$
\left\{\begin{array}{l}
10 b+c+a=18889, \\
10000 c+a+b=58741 .
\end{array}\right.
$$
Multiplying (2) by 10 and subtracting (1) gives
$$
99999 c+9 a=568521 \text {. }
$$

Solving for $a$ yields $a=63169-11111 c$.
Since $a$ is the last four digits of a QQ number, then $0 \leqslant a<10000$.
Thus, $0 \leqslant 63169-11111 c<10000$.
Solving for $c$ gives $\frac{53169}{11111}<c \leqslant \frac{63}{11} \frac{169}{111}$.
Since $c$ is an integer, $c=5$.
Therefore, $a=7614, b=1127$.
Hence, $m=10000(10 b+c)+a=112757614$. So, the hundred's digit is 6.