Let us assume voltmeter is ideal:-It means voltmeter has infinite resistance and current will not flow in voltmeter.\\\\({ R }_{ eq }\\\\) in upper branch = \\\\({ R }_{ eq }\\\\) in lower branch. So current will get equally divide into both branches.\\\\({ V }_{ A }-{ V }_{ B }=4\ imes 1\\quad (1)\\\\ { V }_{ A }-{ V }_{ D }=16\ imes 1 \\quad (2)\\\\)Subtract 2 and 1\\\\({ V }_{ B }-{ V }_{ D }=12V\\\\)A voltmeter will read 12 V