Answer:
The answer is the first matrix. Image attached.
Step-by-step explanation: Given that Dante is solving the system of equations:
In solving the above system of equations, Dante writes the row echelon form of the matrix. We are to select the correct row echelon of the matrix that he wrote.
We know that a matrix is said to be in row echelon form if the leading entry in each nonzero row is a 1 and each column containing a leading 1 has zeros everywhere else.
In the given options, these conditions are satisfied by the first option only. And also, if we write the solution from this matrix, we will have
r = -1, s = 0 and t = 3.
If we substitute these values in the given system, it will get satisfied.
Thus, the first matrix, attached herewith, is the correct matrix.