Помогите, пожалуйста упростить выражение:

● 1)

$(6 {x}^{2} - 7x + 4) - (4 {x}^{2} - 4x + 18) = 6 {x}^{2} - 7x + 4 - 4 {x}^{2} + 4x - 18 = 2 {x}^{2} - 3x - 14 = 2 {x}^{2} + 4x - 7x - 14 = 2x(x + 2) - 7(x + 2) = (2x - 7)(x + 2)$

● 2)

$(3x + 9) + ( - {x}^{2} - 15x - 40) = 3x + 9 - {x}^{2} - 15x - 40 = - {x}^{2} - 12x - 31$

● 3)

$(10 {a}^{2} - 6a + 5) - ( - 11a + {a}^{3} + 6) = 10 {a}^{2} - 6a + 5 + 11a - {a}^{3} - 6 = 10 {a}^{2} + 5a - {a}^{3} - 1$

● 4)

$(13xy - 11 {x}^{2} + 10 {y}^{2} ) - ( - 15 {x}^{2} + 10xy - 15 {y}^{2} ) = 13xy - 11 {x}^{2} + 10 {y}^{2} + 15 {x}^{2} - 10xy + 15 {y}^{2} = 3xy + 4 {x}^{2} + 25 {y}^{2} =$