What is most often given a value of zero to describe an object’s position on a straight line?

A reference point is most often given a value of 0 to describe an object's position on a straight line

Reference point is most often given a value of zero to describe an object's position on a straight line. Positive or negative is assigned to either the right or left of 0 and then the object's current position or displacement calculated accordingly.

Explanation:

because growing process had stoped after 4-5 year

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.