Carnival Ride (was: exponential)

8 The height above the ground, x metres, of a person on a ride at a carnival at time t seconds after the ride started moving can be modelled by the function x(t) = 6 cos [pi[t]\24] + 6

a How long, in seconds, does the ride take to complete a revolution?

b What is the exact height of the ride when t = 20?

c Write down the minimum and maximum heights reached in metres.

d Sketch the graph of x versus t, 0 ≤ t ≤ 120.

e For what values of t, during the first 60 seconds of the ride, is the height at most 3 metres?

i need help on part e. how do i work out this?