At a certain instant, a coil with a resistance of 0.40 and a selfinductance of 200

At a certain instant, a coil with a resistance of 0.40 Ω and a selfinductance of 200 mH carries a current of 0.30 A that is increasing at the rate of 0.50 A/s. 

(a) What is the potential difference across the coil at that instant? 

(b) Repeat if the current is decreasing at 0.50 A/s.