x^2 + x = (x + 3)(3x - 2) - 2

x^2 = 3x^2 - 2x + 9x - 6 -2

x^2 - 3x^2 = 7x - 8

-2x^2 - 7x + 8 = 0

Умножаем на -1 и решаем через теорему Виета.

2x^2 + 7x - 8 = 0

x1 * x2 = -8

x1 + x2 = -7

x1 = -8

x2 = 1