The current through a 1.1 watts light bulb is given by the equation
[tex]P=U*I \rightarrow I=P/U[/tex]
Thus [tex]I=1.1/1.4=0.786 A[/tex]
The capacity of the battery is
[tex]C=15000 mA*h =15 A*h[/tex]
In words we say that if a current of 15 A is taken from it, it lasts for 1 hour.
If we take a current I=0.786 A the battery lasts a time of
[tex]t=C/I=15/0.786 =19.1 hours[/tex]
