`3)\frac{x^2-4}{x^2-x}:\frac{x-2}{x^3-x^2}(x\ne0)`
`=\frac{(x-2)(x+2)}{x(x-1)}.\frac{x^2(x-1)}{x-2}`
`=\frac{x+2}{1}.\frac{x}{1}`
`=x(x+2)`
`=x^2+2x`
`4)\frac{3x-3y}{x-1}:\frac{x^2+x-xy-y}{x^2-1}(x\ne+-1)`
`=\frac{3(x-y)}{x-1}.\frac{(x-1)(x+1)}{x(x+1)-y(x+1)}`
`=\frac{3(x-y)}{1}.\frac{x+1}{(x-y)(x+1)}`
`=\frac{3}{1}.\frac{1}{1}`
`=3`