Provide an Appropriate Response $\mathrm { f } ( \mathrm { x } , \mathrm { y } , \mathrm { z } )$

Provide an appropriate response.
-If $\mathrm { f } ( \mathrm { x } , \mathrm { y } , \mathrm { z } )$ is differentiable, $\mathrm { x } = \mathrm { r } - \mathrm { s } , \mathrm { y } = \mathrm { s } - \mathrm { t }$ , and $\mathrm { z } = \mathrm { t } - \mathrm { r }$ , show that $\frac { \partial f } { \partial r } + \frac { \partial f } { \partial s } + \frac { \partial f } { \partial t } = 0$