(5x^4-9x^3+7x-1)+(-8x^4+4x^2-3x+2)-(-4x^3+5x-1)(2x-7)
Distribute the signs and solve the multiplication
5x^4-9x^3+7x-1-8x^4+4x^2-3x+2 - (-8x^4-28x^3+10x^2-35x-2x+7)
5x^4-9x^3+7x-1-8x^4+4x^2-3x+2 +8x^4+28x^3-10x^2+35x+2x-7
Combine like terms
5x^4-8x^4+8x^4-9x^3+28x^3+4x^2-10x^2+7x-3x+35x-2x-1+2-7
5x^4+19x^3-6x^2+23x-9