3.5x(4x-30)=665

Solution for 3.5x(4x-30)=665 equation:

3.5x(4x-30)=665

We move all terms to the left:

3.5x(4x-30)-(665)=0

We multiply parentheses

12x^2-90x-665=0

a = 12; b = -90; c = -665;
Δ = b2-4ac
Δ = -902-4·12·(-665)
Δ = 40020
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:

$\sqrt{\Delta}=\sqrt{40020}=\sqrt{4*10005}=\sqrt{4}*\sqrt{10005}=2\sqrt{10005}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-90)-2\sqrt{10005}}{2*12}=\frac{90-2\sqrt{10005}}{24}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-90)+2\sqrt{10005}}{2*12}=\frac{90+2\sqrt{10005}}{24}
$