`a)` `\frac{2x(1-x)}{x^2-25}+x-1x+5-x+15-x`
`=\frac{2x-2x^2}{x^2-25}-2x+20`
`=\frac{2x-2x^2-2x(x^2-25)+20(x^2-25)}{x^2-25}`
`=\frac{2x-2x^2-2x^3+50x+20x^2-500}{x^2-25}`
`=\frac{-2x^3+18x^2+52x-500}{x^2-25}`
`b)` `\frac{4}{x+2}+3x-2+5x+24-x^2`
`=\frac{4}{x+2}+8x+22-x^2`
`=\frac{4+8x(x+2)+22(x+2)-x^2(x+2)}{x+2}`
`=\frac{4+8x^2+16x+22x+44-x^3-2x^2}{x+2}`
`=\frac{-x^3+6x^2+38x+48}{x+2}`