Choose the Symmetric Offset command 
.
In the Symmetric Offset Options dialog box, set the options for the symmetric offset, and then click OK.
Tip:
If the Symmetric Offset Options dialog does not appear, on the Symmetric Offset command bar, click the Symmetric Offset Options button to activate the dialog box.
Click the element or elements you want to offset.
On the Symmetric Offset command bar, click the Accept button.