20=a+3a+3a(2)

Solution for 20=a+3a+3a(2) equation:

20=a+3a+3a(2)

We move all terms to the left:

20-(a+3a+3a(2))=0

We add all the numbers together, and all the variables

-(+4a+3a^2)+20=0

We get rid of parentheses

-3a^2-4a+20=0

a = -3; b = -4; c = +20;
Δ = b2-4ac
Δ = -42-4·(-3)·20
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-16}{2*-3}=\frac{-12}{-6}
=+2
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+16}{2*-3}=\frac{20}{-6}
=-3+1/3
$