-12=7m^2+20m

Solution for -12=7m^2+20m equation:

-12=7m^2+20m

We move all terms to the left:

-12-(7m^2+20m)=0

We get rid of parentheses

-7m^2-20m-12=0

a = -7; b = -20; c = -12;
Δ = b2-4ac
Δ = -202-4·(-7)·(-12)
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-8}{2*-7}=\frac{12}{-14}
=-6/7
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+8}{2*-7}=\frac{28}{-14}
=-2
$