If \( \displaystyle \lim_{x \to 1^{+}} \frac{(x-1)\big(6+\lambda \cos(x-1)\big)+\mu \sin(1-x)}{(x-1)^3} = -1 \), where \( \lambda, \mu \in \mathbb{R} \), then \( \lambda + \mu \) is equal to:
\( 17 \)
\( 20 \)
\( 19 \)
\( 18 \)