Answer
$-0.000031 Amp/s$ or, $-3.1 \times 10^{-5}$
Work Step by Step
Apply the chain rule: $\dfrac{dV}{dt}=V_I(\dfrac{dI}{ dt})+V_r(\dfrac{dR}{dt})$
Now, $\dfrac{dV}{dt}=R(\dfrac{dI}{ dt})+I(\dfrac{dR}{dt})$
Plug in the values into the above equation.
$-(0.1)=(400)(\dfrac{dI}{ dt})+(0.08) \times (0.03)$
or, $-(0.1)=(0.00240)+(400) (\dfrac{dI}{ dt})$
Thus, we have $\dfrac{dI}{dt}=-0.000031 Amp/s$ or, $-3.1 \times 10^{-5}$
