6. Упрощенное выражение будет равно -6m - 1. И если подставить, то будет 4.

[tex]6)(5m - 1)(m + 1) - 5m(m + 2)[/tex]
[tex] {5m}^{2} + 5m - m - 1 - {5m}^{2} - 10m \ = - 6m - 1[/tex]
[tex] - 6 times ( - 1 frac{5}{6} ) - 1 = - 6 times ( - frac{11}{6} ) \ - 1 = 11 - 1 = 10[/tex]
[tex]7)(2x - 5y)( - 4x - 3y) - \ (x + 2y)( - 5x + 6y) = [/tex]
[tex] - 8x {}^{2} - 6xy + 20xy + 15 {y}^{2} \ - ( { - 5x}^{2} + 6xy - 10xy + {12y}^{2} ) = [/tex]
[tex] { - 8x}^{2} + 14xy + {15y}^{2} + {5x}^{2} \ + 4xy - 12 {y}^{2} = - 3 {x}^{2} + 18xy \ + {3y}^{2} [/tex]