`C=(\sqrt{x}/(3+\sqrt{x})+(x+9)/(9-x)):((3\sqrt{x}+1)/(x-3\sqrt{x})-1/x)`
`=(\sqrt{x}/(3+\sqrt{x})-(x+9)/((\sqrt{x}-3)(\sqrt{x}+3))):((3\sqrt{x}+1)/(\sqrt{x} (\sqrt{x}-3))-1/x)`
`=(\sqrt{x}(\sqrt{x}-3)-x-9)/((\sqrt{x}-3)(\sqrt{x}+3)):(3x\sqrt{x}+x-\sqrt{x}(\sqrt{x}-3))/(x\sqrt{x}(\sqrt{x}-3))`
`=(x-3\sqrt{x}-x-9)/((\sqrt{x}-3)(\sqrt{x}+3)).(x\sqrt{x}(\sqrt{x}-3))/(3x\sqrt{x}+x-x-3\sqrt{x})`
`=(-3(\sqrt{x}+3))/((\sqrt{x}-3)(\sqrt{x}+3)).(x\sqrt{x}(\sqrt{x}-3))/(3x\sqrt{x}-3\sqrt{x})`
`=(-3x\sqrt{x})/(3\sqrt{x}(x-1))`
`=-x/(x-1)`
