Create three methods:
1. inchesToCentimeters() takes the number entered by the user, and returns the
result of the number multiplied by 2.54.
In your requirements it shows the name of the method you are to create, "inchesToCentimeters". It shows an empty parameter list, "()", but NOTE that this is often shown as empty but is left for you to figure out what, if any, parameters will be required. In your case the parameter is specified in your requirements. Note that the return type is also not shown but it is specified.
You can google tutorials on how to create methods: java method tutorial
Heres one: https://www.w3schools.com/java/java_methods.asp