In Exercises $15-18$ , fill in the blanks using elementary row operations to form a row-equivalent matrix.
$$
\begin{array}{l}{\left[\begin{array}{ccc}{1} & {4} & {3} \\ {2} & {10} & {5}\end{array}\right]} \\ {\left[\begin{array}{rrr}{1} & {4} & {3} \\ {0} & {} & {-1}\end{array}\right]}\end{array}
$$