2*a*0.4*B=50

Solution for 2*a*0.4*B=50 equation:

2a*0.4*=50

We move all terms to the left:

2a*0.4*-(50)=0

Wy multiply elements

0.8a^2-50=0

a = 0.8; b = 0; c = -50;
Δ = b2-4ac
Δ = 02-4·0.8·(-50)
Δ = 160
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{160}=\sqrt{16*10}=\sqrt{16}*\sqrt{10}=4\sqrt{10}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{10}}{2*0.8}=\frac{0-4\sqrt{10}}{1.6}
=-\frac{4\sqrt{10}}{1.6}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{10}}{2*0.8}=\frac{0+4\sqrt{10}}{1.6}
=\frac{4\sqrt{10}}{1.6}
$