Given that $0 < \mathrm { x } < \pi$,
$$\sin ^ { 4 } x = \cos ^ { 4 } x$$
What is the sum of the $\mathbf { x }$ values that satisfy this equality?\\
A) $\frac { 3 \pi } { 2 }$\\
B) $\frac { 4 \pi } { 3 }$\\
C) $\frac { 5 \pi } { 4 }$\\
D) $\pi$\\
E) $2 \pi$