Chapter 3.3B, Problem 10A

Find the missing digits in each of the following subtraction problems.

a. $\begin{array}{r}\underset{\_}{\begin{array}{ccc}3& \text{\_}& \text{\_}\\ -1& 5& 9\end{array}}\\ \begin{array}{ccc}\text{\_}& 2& 4\end{array}\end{array}$ b. $\begin{array}{r}\underset{\_}{\begin{array}{ccccc}1& \underset{\_}{}& \underset{\_}{}& \underset{\_}{}& 6\\ -& 8& 3& 0& 9\end{array}}\\ \begin{array}{ccccc}& 4& 9& 8& 7\end{array}\end{array}$