-30*d+5*d^2+214=234

Solution for -30*d+5*d^2+214=234 equation:

-30d+5d^2+214=234

We move all terms to the left:

-30d+5d^2+214-(234)=0

We add all the numbers together, and all the variables

5d^2-30d-20=0

a = 5; b = -30; c = -20;
Δ = b2-4ac
Δ = -302-4·5·(-20)
Δ = 1300
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1300}=\sqrt{100*13}=\sqrt{100}*\sqrt{13}=10\sqrt{13}$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-10\sqrt{13}}{2*5}=\frac{30-10\sqrt{13}}{10}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+10\sqrt{13}}{2*5}=\frac{30+10\sqrt{13}}{10}
$