CM = 4CM

The image shows a ruler with markings. There are boxes to fill in values. The text 'CM = 4CM' is visible. This appears to be a fill-in-the-blank question related to measurement. Without further context or a complete question, it's impossible to provide a specific numerical answer. However, if the intention is to represent a length of 4 centimeters, the box before 'CM' would be filled with '4'.