.
(a) For case (a), the radius of the circle of latitude is one half of the Earth radius,
and the traveled distance is half of the circumference of this circle.
So, the traveled distance is one fourth of the equator circumference.
From my school years, I remember that the equator circumference is about 40,000 kilometers.
So, the answer to this question is
"the travel distance is one fourth of the equator circumference, or about 10,000 kilometers".
(b) In case (b), the circle is a large circle of the Earth sphere, and the traveled distance is one sixth of its circumference.
So, the answer in this case is
"the travel distance is one sixth of the equator circumference, or about kilometers = 6,666 kilometers".
Thus we revealed that the route through the North pole is shorter in this case than along the altitude (!)
It may seem unexpected, but it is TRUE (!)
Probably, I will surprise you EVEN MORE, if I say that the route through the North Pole
is the SHORTEST route on the Globe between the given points in this case (!) (!) (!)
It is, probably, EVEN MORE unexpected, but it is TRUE, again.
Come again to this form soon to learn something new (!)