Ans: $0.8\text{ litres}$
Let $x$ litres and $y$ litres be the capacity of the bottle and the cup respectively.
Let $x$ litres and $y$ litres be the capacity of the bottle and the cup respectively.
$\left\{ \begin{array}{ll}
x:y = 4:3 & \ldots \unicode{x2460} \\
7x+9y = 11 & \ldots \unicode{x2461}
\end{array} \right.$
From $\unicode{x2460}$,
$\begin{array}{rcl}
\dfrac{x}{y} & = & \dfrac{4}{3} \\
y & = & \dfrac{3x}{4}~\ldots \unicode{x2462}
\end{array}$
Sub. $\unicode{x2462}$ into $\unicode{x2461}$,
$\begin{array}{rcl}
7x+9(\dfrac{3x}{4}) & = & 11 \\
28x +27x & = & 44 \\
55x & = & 44 \\
x & = & \dfrac{4}{5}
\end{array}$
Therefore, the capacity of the bottle is $0.8$ litres.
