-216=3x^2+51x

Solution for -216=3x^2+51x equation:

-216=3x^2+51x

We move all terms to the left:

-216-(3x^2+51x)=0

We get rid of parentheses

-3x^2-51x-216=0

a = -3; b = -51; c = -216;
Δ = b2-4ac
Δ = -512-4·(-3)·(-216)
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-51)-3}{2*-3}=\frac{48}{-6}
=-8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-51)+3}{2*-3}=\frac{54}{-6}
=-9
$