a) this is the simplified form
[tex]( {x}^{3} + 3 {x}^{2} - 6) + ( {x}^{2} - x + 7) \\ = {x}^{3} + 3 {x}^{2} - 6 + {x}^{2} - x + 7 \\ = {x}^{3} + 4 {x}^{2} - x + 1[/tex]
b)
[tex](5 {x}^{2} - 4x + 7) - ( {x}^{2} - 2x - 5) \\ = 5 {x}^{2} - 4x + 7 - {x}^{2} + 2x + 5 \\ = 4 {x}^{2} - 2x + 12[/tex]
