28=(6+x)(4-0.25x)

Solution for 28=(6+x)(4-0.25x) equation:

28=(6+x)(4-0.25x)

We move all terms to the left:

28-((6+x)(4-0.25x))=0

We add all the numbers together, and all the variables

-((x+6)(-0.25x+4))+28=0

We multiply parentheses ..

-((+0x^2+4x+0x+24))+28=0


We calculate terms in parentheses: -((+0x^2+4x+0x+24)), so:

(+0x^2+4x+0x+24)

We get rid of parentheses

0x^2+4x+0x+24

We add all the numbers together, and all the variables

x^2+5x+24

Back to the equation:

-(x^2+5x+24)


We get rid of parentheses

-x^2-5x-24+28=0

We add all the numbers together, and all the variables

-1x^2-5x+4=0

a = -1; b = -5; c = +4;
Δ = b2-4ac
Δ = -52-4·(-1)·4
Δ = 41
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-\sqrt{41}}{2*-1}=\frac{5-\sqrt{41}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+\sqrt{41}}{2*-1}=\frac{5+\sqrt{41}}{-2}
$