Problem 4-62 Centripetal acceleration

An astronaut in training is spinning around in a device that rotates at 30 revolutions per minute. (a) If the astronaut is $7.5\; m$ from the centre of the device, what is the magnitude of the centripetal acceleration? (b) Express the answer in terms of "$g,$" the magnitude of the acceleration due to gravity.
[Ans. (a) $74\; m/s^2$   (b) $7.6\; g$]

The expression for centripetal acceleration is: 

(A)  $a_c = v^2/r$

(B)  $a_c = 4\pi ^2r/T^2$