#### Answer

Add $3$ times row (2) to row (3) to transform the first matrix into the second matrix.
To reverse this operation, add $-3$ times row (2) to row (3) in the second matrix to get back the original matrix.

#### Work Step by Step

Recall from the bottom of page 6 and the top of page 7 that all elementary row operations are reversible. Moreover, there are only three such operations: (1) swapping two rows, (2) multiplying a row by a nonzero constant, and (3) adding a constant multiple of one row to another row.