$3(x - 7)^2 - 2(x + 7)(x - 2) = (x + 11)(x - 4) + 101$
$3(x^2 - 14x + 49) - 2(x^2 + 7x - 2x - 14) = x^2 + 11x - 4x - 44 + 101$
$3x^2 - 42x + 147 - 2x^2 - 14x + 4x + 28 = x^2 + 11x - 4x + 57$
$3x^2 - 2x^2 - x^2 - 42x - 14x + 4x - 11x + 4x = 57 - 147 - 28$
−59x = −118
x = −118 : −59
x = 2

$2x(x + 3)^2 - 3x(x - 1)(x + 8) = x^2(-x - 9) + 21$
$2x(x^2 + 6x + 9) - 3x(x^2 - x + 8x - 8) = -x^3 - 9x^2 + 21$
$2x^3 + 12x^2 + 18x - 3x^3 + 3x^2 - 24x^2 + 24x = -x^3 - 9x^2 + 21$
$(2x^3 + x^3 - 3x^3) + (12x^2 + 3x^2 - 24x^2 + 9x^2) + (18x + 24x) = 21$
42x = 21
x = 21 : 42
x = 0,5

$y(2y - 5)(2y + 5) - 4y(y + 6)^2 = 13 - 48y^2$
$y(4y^2 - 25) - 4y(y^2 + 12y + 36) = 13 - 48y^2$
$4y^3 - 25y - 4y^3 - 48y^2 - 144y + 48y^2 = 13$
$(4y^3 - 4y^3) + (-48y^2 + 48y^2) + (-25y - 144y) = 13$
−169y = 13
$y = -\frac{13}{169} = -\frac{1}{13}$