Just trying to work out what I'm doing wrong here to find the average angular acceleration.

I used angular acceleration = final velocity - initial velocity all divided by the time pasted.

(Also converted units from rpm to rad/s

^{2}by multiplying by (2∏/60)

So far my initial answer is 0.11 rad/s

^{2}which is apparently wrong, any idea what I can be doing wrong here?