Flow of water thorough an equal percentage valve is $900 \text{ litre } h^{-1}$ at $30 \%$ opening, and $1080 \text{ litre } h^{-1}$ at $35 \%$ opening. Assume that the pressure drop across the valve remains constant. The flow rate (in $\text{ litre } h^{-1}$) through the valve at $45\%$ opening is ________ (round off to nearest integer)