The current in a series RL circuit

[BryceHarper]

Homework Statement

The current in a series RL circuit increases to 20% of its final value in 3.4μs. If L = 2.0mH, what is the resistance R?

Homework Equations

I=I_0(1-e^(-t/(L/R))) <----Im not sure if this equation is right?

The Attempt at a Solution

I'm unsure how to start this problem, or if I'm on the right track with this equation?

 

[haruspex]

The current in a series RL circuit increases to 20% of its final value in 3.4μs. If L = 2.0mH, what is the resistance R?
I=I_0(1-e^(-t/(L/R))) <----Im not sure if this equation is right?

Neither do I, but assuming it is...
In terms of the variables in that equation, what would be the final value, and what would be the value after 3.4μs?