Из первого 3х-4 = у
4х^2 - 3x(3x-4) -(3x-4)^2 = 6
4x^2 - 9x^2 +12x -(9x^2 - 24x +16) -6 =0
4x^2 - 9x^2 +12x -9x^2 + 24x -16 -6 =0
-14x^2 + 36x - 22 = 0
7x^ 2 - 18x + 11 = 0
D = -18^ 2 -4*7*11 =16
x 12 = (18 +- 4)/ 14
x1 = 1 y1 = 3* 1 -4 = -1
x2 = 11/7 = 1 4/7 y 2 = 3* 11/7 -4 = 5/7