How many coulombs of charge enter a 1.00 cm length of the axon during this process?

Let me explain the process and then you do the maths: 
First: Find the number of ions crossing the lenght like this
 5.6 x10^11 x 1 x10^-2
The resul of that you use it for quantization of charge crossing like this:
Previous result   x 1.6 x10^-19
The result will give you the amount of coulombs you need