12=15b2-6b

Solution for 12=15b2-6b equation:

12=15b^2-6b

We move all terms to the left:

12-(15b^2-6b)=0

We get rid of parentheses

-15b^2+6b+12=0

a = -15; b = 6; c = +12;
Δ = b2-4ac
Δ = 62-4·(-15)·12
Δ = 756
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{756}=\sqrt{36*21}=\sqrt{36}*\sqrt{21}=6\sqrt{21}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-6\sqrt{21}}{2*-15}=\frac{-6-6\sqrt{21}}{-30}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+6\sqrt{21}}{2*-15}=\frac{-6+6\sqrt{21}}{-30}
$