How would you use this relationship to investigate the amount of oxygen being produced if we can only measure change in the amount of carbon dioxide moving in and out of the plant in the forest

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