Solve the system of equation 3y+2z=12 andy-z=9

The two equations given are:
3y + 2z = 12
y - z = 9
Now let us take the second equation first and find the value of y in relation to z
y = 9 + z
Now we will put the value of y found from the second equation in the first equation.
3y + 2z = 12
3(9 + z) + 2z = 12
27 + 3z + 2z = 12
5z = 12 - 27
5z = -15
z = -(15/5)
   = -3
Now again we will put the value of z in the second equation for finding the value of y
y = 9 + z
  =  9 - 3
  = 6
So we find the value of "y" is 6 and that of "z" is -3