I need help with the following problem.

**A skater does a pirouette at the rate of 2.0 rev / second and then stop within 3/4 rev. Assume that the angular decceleration is constant and calculate its magnitude.**

I tried to compute it but I found -18 rad/s[sup]2[/sup].

BUt the textbook gives -17 rad/s[sup]2[/sup].

Please can someone help me with this problem?

Thank you

B