Solving 3 variable systems of equations by substitution

Solving Three Variable Systems of Equations – (Easy)
Solve the following system of equations by substitution:

$2x + 3y + 4z = 0$

$2y + 3z = 23$

$z = 5$
Solving Three Variable Systems of Equations – (Medium)
Solve the following system of equations by substitution:

$3x - 5y + z = 0$

$x - 2y - z = 0$

$z = -2$
Solving Three Variable Systems of Equations – (Hard)
Solve the following system of equations by substitution:

$15x + 7y - 6z = -9$

$5x - 3y + 6z = 13$

$z = 4$