Use the Chain Rule to Find $\frac { \partial u } { \partial p }$

Multiple Choice

Use the Chain Rule to find $\frac { \partial u } { \partial p }$ . $u = \frac { x + y } { y + z }$ $x = p + 5 r + 7 t , y = p - 5 r + 7 t , z = p + 5 r - 7 t$

A) $\frac { \partial u } { \partial p } = - \frac { 7 t } { p ^ { 2 } }$
B) $\frac { \partial u } { \partial p } = \frac { 7 t } { p }$
C) $\frac { \partial u } { \partial p } = - \frac { 5 t } { p ^ { 3 } }$
D) $\frac { \partial u } { \partial p } = - \frac { 35 t } { p ^ { 2 } }$
E) $\frac { \partial u } { \partial p } = \frac { 35 t } { p ^ { 2 } } + t$