On using elementary row operations R1 → R1 - 3R2 in the following matrix equation

The elementary row operation R1 → R1 - 3R2 is used to subtract three times the second row from the first row in the matrix equation. This operation is used to eliminate the coefficient of a variable of one equation, in this case the variable x2, from the other equation, in this case x1. After subtracting 3 times the second row from the first row, the variable x2 will no longer be expressed in the first equation.