A) \frac{b}{a+b}* \frac{a^{2} -b^{2} }{b^{2} }=\frac{b}{a+b} *\frac{(a+b)(a-b) }{b^{2} } = \frac{b*(a+b)(a-b)}{(a+b)*b^{2} } = \frac{a-b}{b}
b) \frac{2x-2y}{y}: \frac{ x^{2} - y^{2} }{y} =\frac{(2x-2y)y}{y(x-y)(x+y)} = \frac{2(x-y)y}{y(x-y)(x+y)}= \frac{2}{x+y}
c) (- \frac{2 a^{2} }{b})^3= - \frac{8a ^6}{b ^3}
d)3ab * \frac{a ^2}{b} = \frac{3ab*a ^2}{b} = 3a^3