13)

Step 1:

The equations are

Solve by using substitution method.

Substitute in

Solution:

The solution is

15)

Step 1:

The system of equations are

Solve by using elimination method.

Write the equations into matrix form ,

Write the equations into matrix form , where is coefficient matrix,

is variable matrix and is constant matrix.

The augmented matrix is .

The augmented matrix is

Solution:

The solutions of equations are

33)

Step 1:

The equations are

Solve by using substitution method.

Substitute in

Solution:

The solution is