PLEASE HELP: a ferris wheel with a radius of 20 m rotates once every 40 s. A passenger gets on at the lowest point which is 1 m above the ground. This situation can be modelled by the equation:
where h is the distance above the ground in metres and t is the time in seconds.

Determine the times (accurate to one decimal place) in the first cycle when the height of the passenger is 15 m or higher. An algebraic solution is required