how can i hide this column as hidden option is greyed out(not available).
To hide any list column follow these steps:
1. Go to List Settings > Advanced Settings
2. Select option 'Yes' for Allow management of content types?
3. Now, in List Settings, go to 'Item' content type in Content Types section.
4. In Columns section click on the column you want to make hidden.
5. In Column Settings > Select Hidden option > OK
To hide Calculated column follow this: Hide Calculated Column in SharePoint 2013
- Open SharePoint Designer.
- Open the website that contains your list with the calculated column.
- Click on "Lists and Libraries" in the left column (under Site Objects).
- On the right, click on the list that contains your calculated column. Under "Content Types", click on the content type where you want to hide the calculated column
- In the content type screen, click "Edit content type columns"
- In the column "Property", try clicking a few times on the "Optional" value until it changes into a dropdown list.
- Select "Hidden" from the dropdown list and click on push changes to sites and lists on ribbon.
- Finally Save your changes.
Reference: Hide Calculated Column in SharePoint 2013