The diameter is 50 meters, so the radius = 25 m, and this is the amplitude (the first blank). Since the entrance is at the low point of 4 m above the ground, this is the vertical shift (the last blank). If it takes 6 mins for 3 revolutions, then the period is 6/3 = 2 mins/revolution. The function sin (bt) is calculated as b = 2pi/period = pi, so b = 1. At t = 0, the sin function should be at the minimum, which is normally at sin (3pi/2).
Therefore the complete funciton is:
h(t) = 25sin(pi*t + 3/2*pi) + 4