0=21m+8-9m^2

Solution for 0=21m+8-9m^2 equation:

0=21m+8-9m^2

We move all terms to the left:

0-(21m+8-9m^2)=0

We add all the numbers together, and all the variables

-(21m+8-9m^2)=0

We get rid of parentheses

9m^2-21m-8=0

a = 9; b = -21; c = -8;
Δ = b2-4ac
Δ = -212-4·9·(-8)
Δ = 729
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{729}=27$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-27}{2*9}=\frac{-6}{18}
=-1/3
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+27}{2*9}=\frac{48}{18}
=2+2/3
$