The third equation has only two variables and we can substitute z-20 for y in the other two equations: 1.5x+5.75(z-20)+2.6z=598.5 and x+z-20+z=200. These simplify to: 1.5x+8.35z=713.5 and x+2z=220. So x=220-2z, which we can substitute to get 1.5(220-2z)+8.35z=713.5. 5.35z=383.5, so z=7670/107. From this we find y=7670/107-20=5530/107 and x=8200/107. These values in approximate decimals are: x=76.64, y=51.68, z=71.68.