((16+6x)÷2)×x=528 equation

Move right part of the equation to
left part with negative sign.

The equation is transformed from
$$x \frac{6 x + 16}{2} = 528$$
to
$$x \frac{6 x + 16}{2} - 528 = 0$$
Expand the expression in the equation
$$x \frac{6 x + 16}{2} - 528 = 0$$
We get the quadratic equation
$$3 x^{2} + 8 x - 528 = 0$$
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 - it is the discriminant.
Because
$$a = 3$$
$$b = 8$$
$$c = -528$$
, then

D = b^2 - 4 * a * c = 

(8)^2 - 4 * (3) * (-528) = 6400

Because D > 0, then the equation has two roots.

x1 = (-b + sqrt(D)) / (2*a)

x2 = (-b - sqrt(D)) / (2*a)

or
$$x_{1} = 12$$
$$x_{2} = - \frac{44}{3}$$