$$-4m^{6}n^{7}n\left(-2\right)m^{2}n^{6}$$
To multiply powers of the same base, add their exponents. Add $6$ and $2$ to get $8$.$$-4m^{8}n^{7}n\left(-2\right)n^{6}$$
To multiply powers of the same base, add their exponents. Add $7$ and $1$ to get $8$.$$-4m^{8}n^{8}\left(-2\right)n^{6}$$
To multiply powers of the same base, add their exponents. Add $8$ and $6$ to get $14$.$$-4m^{8}n^{14}\left(-2\right)$$
Multiply $-4$ and $-2$ to get $8$.$$8m^{8}n^{14}$$