Answer :
see the attached figure
the points A, B and C are collinear (the three points lies on the same line)
so
AC=AB+BC ------> by addition segment postulate
the total length is equal to the sum of its parts

see the attached figure
the points A, B and C are collinear (the three points lies on the same line)
so
AC=AB+BC ------> by addition segment postulate
the total length is equal to the sum of its parts