a) \(\frac{3m-6n}{10n-5m}\)
\(=\frac{-3\left(2n-m\right)}{5\left(2n-m\right)}=\frac{-3}{5}\)
b) \(\frac{y^3+y^2+4y+4}{y^2+2y-8}\)
\(=\frac{y^2\left(y+1\right)+4\left(y+1\right)}{y^2+2y+1-9}\)
\(=\frac{\left(y^2+4\right)\left(y+1\right)}{\left(y+1\right)^2-9}\)
\(=\frac{\left(y^2+4\right)\left(y+1\right)}{\left(y-2\right)\left(y+4\right)}\)
c) \(\frac{x^2-xy-xz+yz}{x^2+xy-xz-yz}\)
\(=\frac{x\left(x-y\right)-z\left(x-y\right)}{x\left(x+y\right)-z\left(x+y\right)}\)
\(=\frac{\left(x-z\right)\left(x-y\right)}{\left(x-z\right)\left(x+y\right)}\)
\(=\frac{x-y}{x+y}\)
