Answer
$9x^2-3x+5$.
Work Step by Step
In the equation form
$A-(4x^2+2x-3)=5x^2-5x+8$
Add to both sides $(4x^2+2x-3)$.
$A-(4x^2+2x-3)+(4x^2+2x-3)=5x^2-5x+8+(4x^2+2x-3)$
Simplify.
$A=5x^2-5x+8+4x^2+2x-3$
Add like terms.
$A=9x^2-3x+5$.