Observe the ruler, it is marked in centimeters. \

The long marks are centimeters, and the shorter marks are millimeters and there are 10 millimeters (mm) for each centimeter (cm).

The point X starts at 0^th short mark and point Y ends at 38^th short mark.

Length of the line segment = 38 millimetres.

= 30 mm + 8 mm                              (Rewrite 38 as 30 + 8)

= 3cm + 0.8 cm                                  (10 millimetres = 1 centimetre)

= 3.8 cm 

The length of the line segment .