Three bulbs, each with a resistance of 180 , are connected in...

When only one bulb is switched on, the circuit is completed only through that single bulb.

The effective resistance of the circuit is equal to the resistance of one bulb, $R = 180 \Omega$.

The emf of the ideal battery is $V = 60 \text{ V}$.

Using Ohm's law, the current delivered by the battery is given by:

$I = \dfrac{V}{R}$

$I = \dfrac{60}{180} = \dfrac{1}{3} \text{ A}$

$I \approx 0.33 \text{ A}$