(8-2x)(6-x)-30=0 equation

Expand the expression in the equation
$$\left(\left(- x + 6\right) \left(- 2 x + 8\right) - 30\right) + 0 = 0$$
We get the quadratic equation
$$2 x^{2} - 20 x + 18 = 0$$
This equation is of the form
$$a\ x^2 + b\ x + c = 0$$
A quadratic equation can be solved using the discriminant
The roots of the quadratic equation:
$$x_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$x_{2} = \frac{- \sqrt{D} - b}{2 a}$$
where $D = b^2 - 4 a c$ is the discriminant.
Because
$$a = 2$$
$$b = -20$$
$$c = 18$$
, then
$$D = b^2 - 4\ a\ c = $$
$$\left(-1\right) 2 \cdot 4 \cdot 18 + \left(-20\right)^{2} = 256$$
Because D > 0, then the equation has two roots.
$$x_1 = \frac{(-b + \sqrt{D})}{2 a}$$
$$x_2 = \frac{(-b - \sqrt{D})}{2 a}$$
or
$$x_{1} = 9$$
Simplify
$$x_{2} = 1$$
Simplify