B=4a+9a^2

Solution for B=4a+9a^2 equation:

=4B+9B^2

We move all terms to the left:

-(4B+9B^2)=0

We get rid of parentheses

-9B^2-4B=0

a = -9; b = -4; c = 0;
Δ = b2-4ac
Δ = -42-4·(-9)·0
Δ = 16
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$B_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$B_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{16}=4$
$B_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-4}{2*-9}=\frac{0}{-18}
=0
$
$B_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+4}{2*-9}=\frac{8}{-18}
=-4/9
$