(7x-21)+3x(4x-9)=180

Solution for (7x-21)+3x(4x-9)=180 equation:

(7x-21)+3x(4x-9)=180

We move all terms to the left:

(7x-21)+3x(4x-9)-(180)=0

We multiply parentheses

12x^2+(7x-21)-27x-180=0

We get rid of parentheses

12x^2+7x-27x-21-180=0

We add all the numbers together, and all the variables

12x^2-20x-201=0

a = 12; b = -20; c = -201;
Δ = b2-4ac
Δ = -202-4·12·(-201)
Δ = 10048
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{10048}=\sqrt{64*157}=\sqrt{64}*\sqrt{157}=8\sqrt{157}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-8\sqrt{157}}{2*12}=\frac{20-8\sqrt{157}}{24}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+8\sqrt{157}}{2*12}=\frac{20+8\sqrt{157}}{24}
$