Simplify : -7m -[3n -8m -(4n - 10m)]

Answer: Option B

$$\begin{array}{rl}& \text{ = }-7m-\left[3n-\left\{8m-\left(4n-10m\right)\right\}\right]\\ & =-7m-\left[3n-\left\{8m-4n+10m\right\}\right]\\ & =-7m-\left[3n-18m+4n\right]\\ & =-7m-\left[7n-18m\right]\\ & =-7m-7n+18m\\ & =11m-7n\end{array}$$