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The distance between the places $A$ and $C$ on a straight road is $300\mathrm{m}$. There is a balloon $B$ above the road between the places $A$ and $C$. See the picture. The angles of elevation from the places $A$ and $C$ to the balloon $B$ are ${20}^{\circ }$ and ${40}^{\circ }$ respectively. What is the height $h$ of the balloon?