How to find a resistor value from a circuit graph

[confuse]

Hello
i would be happy to get some help in this question:

http://webphysics.davidson.edu/physletprob/ch9_problems/ch9_5_circuits/circuits9_5_5.html

i simply have no idea how to use the graph in order to calculate the value of the resistor.
any help would be appreciated.

thanks

 

[rl.bhat]

Find io from the graph. Find the time constant RC = io/e where e = 2.71828.
From RC you can find R.

 

[Thaakisfox]

We know from the theory that the current vs time function is:

$$I(t)=I_0e^{\frac{t}{RC}}$$

Now you can see that when the current is the e-th part of I_0 i.e. I=I_0/e then the time is $$t=RC$$

Now try to calculate R.