0.8X(f+6)=7.2

Solution for 0.8X(f+6)=7.2 equation:

0.8X(X+6)=7.2

We move all terms to the left:

0.8X(X+6)-(7.2)=0

We add all the numbers together, and all the variables

0.8X(X+6)-7.2=0

We multiply parentheses

0X^2+0X-7.2=0

We add all the numbers together, and all the variables

X^2+X-7.2=0

a = 1; b = 1; c = -7.2;
Δ = b2-4ac
Δ = 12-4·1·(-7.2)
Δ = 29.8
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{-(1)-\sqrt{29.8}}{2*1}=\frac{-1-\sqrt{29.8}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{29.8}}{2*1}=\frac{-1+\sqrt{29.8}}{2}
$