6) (70 / x^2-16) - (17 / x-4) = 3x / x+4;

Общий знаменатель (x-4)(x+4) = x^2-16.

70 - 17(x+4) = 3x(x-4)

70 - 17x - 68 = 3x^2 - 12x

2 - 17x = 3x^2 - 12x

3x^2 + 5x - 2 = 0

D = 5^2 - 4(3)(-2) = 25 + 24 = 49

x1 = (-5 + 7) / 6 = 2/6 = 1/3

x2 = (-5 - 7) / 6 = -12/6 = -2