(7m+4)(3m+4)=0

Solution for (7m+4)(3m+4)=0 equation:

(7m+4)(3m+4)=0

We multiply parentheses ..

(+21m^2+28m+12m+16)=0

We get rid of parentheses

21m^2+28m+12m+16=0

We add all the numbers together, and all the variables

21m^2+40m+16=0

a = 21; b = 40; c = +16;
Δ = b2-4ac
Δ = 402-4·21·16
Δ = 256
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{256}=16$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(40)-16}{2*21}=\frac{-56}{42}
=-1+1/3
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(40)+16}{2*21}=\frac{-24}{42}
=-4/7
$