a) A + B
\(=4x^5-7y^2+2xy-x-5y-\frac{1}{4}+6x^5-2y^2+3x-\frac{1}{6}y+6\)
\(=\left(4x^5+6x^5\right)-\left(7y^2+2y^2\right)+2xy+\left(3x-x\right)-\left(5y+\frac{1}{6}y\right)+\left(6-\frac{1}{4}\right)\)
\(=10x^5-9y^2+2xy+2x-\frac{31}{6}y+\frac{23}{4}\)
A - B
\(=4x^5-7y^2+2xy-x-5y-\frac{1}{4}-6x^5+2y^2-3x+\frac{1}{6}y-6\)
\(=\left(4x^5-6x^5\right)+\left(2y^2-7y^2\right)+2xy-\left(x+3x\right)+\left(\frac{1}{6}y-5y\right)-\left(\frac{1}{4}+6\right)\)
\(=-2x^5-5y^2+2xy-2x-\frac{29}{6}y-\frac{25}{4}\)