Sun-earth-moon in a straight line. Earth in the 'middle'.
The average velocity of Sandy is given by the total distance covered S divided by the total time taken t:

The total distance covered is

while the total time taken is 2 hours + half an hour (for the rest) + 1 hour and half, so

Therefore, the average velocity is
Answer:
they help us allocate a particular place in case one needs to allocate or find a place or something
Around 70-72% of earth’s surface is covered in water (most of it is salt water).
Hope this helps.