Torque and circular motion

Hi here is the link to the question http://filestore.aqa.org.uk/subjects/AQA-PHYB4-QP-JUN15.PDF

The question i'm stuck on is 1 b ii) The mark scheme says "Angular acceleration, α = 3.6 / 20 OR 3.59 / 20 or 0.18
or 0.1795
3.8 (3.77, 3.78) × 10^4 "
It's a spec B paper (not my spec) but i'm pretty sure i haven't come across angular acceleration so i'm just wondering which equation to use

It is like the "normal constant acceleration" or what people like say SUVAT equation.

v = u + at

ω_f = ω_i + α t

where ω_f is final angular velocity or final angular speed,
ω_i is initial angular velocity or initial angular speed,
α is angular acceleration.