Basic geometry: how can you use a translation to find a missing vertex in a rectangle or square? . i know what a translation is, but i don't understand how the sliding of the figure will me to find missing vetex?

Johnny rode his bike to a friends house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was unable to play. what was his displacement for the total bike ride trip? what could you use as a reference point ? show the steps to solve this problem.