Time-dependent angular acceleration problem

[Ceenaya19]

Homework Statement

As a result of friction, the angular speed of a
wheel changes with time according to
dθ/dt=ω0*e^-σt ,
where ω0 and σ are constants. The angular
speed changes from an initial angular speed
of 3.96 rad/s to 3.46 rad/s in 3.92 s .
Determine the magnitude of the angular
acceleration after 2.44 s.
Answer in units of rad/s2

Homework Equations

dω/dt = \alpha

The Attempt at a Solution

I've tried differentiating the given expression for omega in an attempt to get the angular acceleration, but that didn't work because \sigma is undefined in the problem. I've also tried taking the ln of both sides, but that didn't work either. I tried solving for \sigma in terms of ω and ω0, but that didn't work. Finally, I tried just assuming that the acceleration is just constant from t0 to t, but that also wasn't the right answer. So, I have no idea what to try next...

 

[Ceenaya19]

I still can't get it O_O