Ions moving across a cell membrane

Question: The figures show ions, labeled with their charges, moving in or out through the membranes of four cells. If the ions sall cross the membranes during the same interval of time, how wwould the currents into the cells compare with each other?

Solution:

Cell A has positive current going into it because its charge is increased, i.e. has a positive value of Δq.

Cell B has the same current as cell A, because by losing one unit of negative charge it also ends up increasing its own total charge by one unit.

Cell C's total charge is reduced by three units, so it has a large negative current going into it.

Cell D loses one unit of charge, so it has a small negative current into it.