Algebra

We can use the Quadratic formula to find the value of v. 

a = 5, b = 21, c = v

$\frac{-21-\sqrt{201}}{10} = {-b \pm \sqrt{b^2-4ac} \over 2a}$

$\frac{-21-\sqrt{201}}{10} = {-21 \pm \sqrt{21^2-4(5)(v)} \over 2(5)}$

$\frac{-21-\sqrt{201}}{10} = {-21 - \sqrt{441-20v} \over 10}$

$\sqrt{201} = \sqrt{441-20v}$

$201 = 441-20v$

$20v = 240$

$\mathbf{v=12}$

Therefore, the value of v is 12