Answer
$$\dfrac{dI}{dt}=-0.000031 Amp/s \\=-3.1 \times 10^{-5}$$
Work Step by Step
We need to use chain rule as follows: $\dfrac{dV}{dt}=V_I(\dfrac{dI}{ dt})+V_r(\dfrac{dR}{dt})$
Now, $\dfrac{dV}{dt}=R(\dfrac{dI}{ dt})+I(\dfrac{dR}{dt}) .....(1)$
Now, we will plug the values in the equation (1).
$-(0.1)=(400) \times (\dfrac{dI}{ dt})+(0.08) \times (0.03)$
or, $-(0.1)=(0.00240)+(400) \times (\dfrac{dI}{ dt})$
Thus, we have $$\dfrac{dI}{dt}=-0.000031 Amp/s \\=-3.1 \times 10^{-5}$$
