На высоте 3,5 км ............
4 (x^2 - 2x + 1) = x^2 + 4x + 4
4x^2 - 8x + 4 = x^2 + 4x + 4
4x^2 - 8x - x^2 - 4x = 0
3x^2 - 12x = 0 // : 3
x^2 - 4x = 0
x (x - 4) = 0
x = 0 ;
x - 4 = 0 ==> x = 4
A (x - y) = x + kl
x - y = (x+ kl)/a
x = (x + kl)/a + y
x = x/a + kl/a + y
x - x/a = kl/a + y
x* (1 - 1/a) = kl/a + y
x = (kl/a + y) / (1 - 1/a)
x = (kl + ay)/ (a - 1)