I work in Maine, but live in another state. Worksheet A asks : "4The number of days I spent in Maine (for any purpose) was" . IK don't know what to put for this.

For the calculation of the number of days you spent in Maine (for any purpose), you should input the number of days you were in the state for work or for any other reason. Any portion of the day is considered a full day. 

The input of the number of days will help determine if you are truly a nonresident of Maine. For income tax purposes, you are considered a resident of Maine if you are not domiciled in Maine for the entire tax year, but have a permanent home in Maine for the entire tax year and spend more than 183 days of the tax year in Maine. 

For more information, please see Individual Income Tax FAQs and Residency Guidance.