The period = 1.5 hrs
The frequency = 1 / period = 1 / 1.5 = 2 / 3
So...in one hour....the satellite makes 2/3 of an orbit [revolution ]
In one day.....the satellite makes 24 / 1.5 = 16 revolutions
The amplitude of the graph is 7000 km......[ 7000 km above the Earth's center ]
I don't understand this sentence ..." Earth’s radius is [25,484], so the satellite is [ 18,484 kilometers away from earth]."
The Earth's radius in km = 6371 km.....so.....the max distance that the satellite is above the Earth's surface is 7000 - 6371 = 629 km