What are biomes, what types of biomes is there ? how many ?

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

Eutrophication caused by human nutrient pollution.

What does the number 18.9984 represent in the image?