What is the sum of the missing digits in the subtraction problem below?

$\begin{array}{llllll} {} &5 & \text{_} & \text{_} & \text{_} & \text{_} \\ – &4 & 8 & \text{_}& 8 & 9 \\ \hline & & 1 & 1 &1 &1 \end{array}$