That's a not-bad description of a capacitor.
Answer:
a). 87.5 mA or
A
b). 1.78 
Explanation:

n the number of free electrons is 28 in text reference and if they don't give q is take as the charge of electron.
a).
A
b).


15 km 30 divided by 4 is 7.5 km in 30 min times that by 2 the answer is 15