Explanation

(c) We know that when current flow is same then resistors are connected in series, hence resultant resistance is
$R^{'} = R_{1} + R_{2} = 10\Omega + 20\Omega = 30\Omega$
Also since, cell are connected in opposite directions, the resultant emf is
$E = E_{1} - E_{2} = 5V - 2V = 3V$
From Ohm’s law $E = iR$
$\therefore\ \ \ i = \frac{E}{R} = \frac{3}{30} = 0.1A$