$4-$The same capacitor circuit is now charged up to $12V$ and the instantaneous voltage is

$v=12(1-e^{-\frac{t}{2}}),eq(5)$

The tasks are to:

a$)$ Differentiate $(v)$ with respect to $(t)$ to find $\frac{dv}{dt}.$

b$)$ Calculate the value of $\frac{dv}{dt}$ at $t=2s$ and $t=4s.$

c$)$ Find the second derivative $(\frac{d^{2}v}{d{t}^2}).$