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