The equations are inconsistent. If you add the first and third equations you get 5x=12. If you double the first equation and add it to the second you get 5x=5. Since 12 is not equal to 5, the equations are inconsistent. The question may have been wrongly transcribed. Also whenever y and z appear, it's as y-z in all equations. There is no independent relationship between y and z that would allow them to be individually calculated.