The length of the line is 2.1 centimeters.
To find the length of the line given in centimeters and millimeters, you need to add the values together. Remember that 1 centimeter is equal to 10 millimeters.
So, the length of the line is:
2 cm+1 mm=2 cm+0.1 cm=2.1 cm
Therefore, the length of the line is 2.1 centimeters.