1) y-8/2y - 3-4y/y^2
= y - 4/y - 3 - 4/y
= (y^2 - 4 - 3y - 4) / y
= (y^2 - 3y - 8) / y

2) 7/a - 56/a^2 + 8a
= 7/a - 56/a^2 + 8a
= (7a - 56 + 8a^3) / a^2
= (8a^3 + 7a - 56) / a^2

3) b/b+1 - b^2/b^2-1
= b/(b+1) - b^2/(b^2-1)
= b/(b+1) - b^2/((b+1)(b-1))
= (b(b-1) - b^2) / ((b+1)(b-1))
= (b^2 - b - b^2) / (b^2 - 1)
= -b / (b^2 - 1)

4) 3x - 15x^2/5x+2
= 3x - 3x(5x+2) / 5x+2
= 3x - 15x^2 - 6x / 5x+2
= (3x - 6x - 15x^2) / 5x+2
= (-3x - 15x^2) / 5x+2