Solve the following system of simultaneous linear equations by substitution method:

3x - 5y = -2

7x - 3y = -9

Solve the following system of simultaneous linear equations by the substitution method:

5x + 4y - 4 = 0

x - 20 = 12y

Solve the following system of simultaneous linear equations by the substitution method:

2x + 3y = 23

5x - 20 = 8y

Solve the following system of simultaneous linear equations by the substitution method:

mx - ny = m² + n²

x + y = 2m