This is another high school geographical question with some math in it,please help me.?

Question

How fast must an aeroplane fly (very close to the earth`s surface) from one point of the equator(indefinite one)to the north pole in 15 hours?
How fast must the plane fly when it`s 100 km above earth and has to do the same way like before(in 15 hours)?
Sorry for my english but it`s not my language and this is just to technichal for me.

Answer 1

It has to travel 1/4 of the earth's circumference or about 6250 miles. To do this in 15 hrs requires the plane to travel 6250/15= 416MPH