A train $300 \mathrm{m}$ long is running at a uniform speed of $20 \mathrm{m}/\mathrm{s}$, then the time taken by it to cross a platform of length $60 \mathrm{m}$ is seconds

The time taken for two trains of lengths, $a$ meters and $b$ meters, running at $x \mathrm{km}/\mathrm{h}$ and $y \mathrm{km}/\mathrm{h}$ in the opposite directions to cross each other $=$Time taken to cover $(a+b)$ meters at _____ $\mathrm{km}/\mathrm{h}$.

Two bodies move away from each other with speeds of $10 \mathrm{km}/\mathrm{h}$ and $5 \mathrm{km}/\mathrm{h}$. Then, their relative speed is _____ $\mathrm{km}/\mathrm{h}$

The time taken by a train $l$ meters long running at $x \mathrm{km}/\mathrm{h}$ to pass a man who is running at $y \mathrm{km}/\mathrm{h}$ in the direction opposite to that of the train. The time taken to cover $l$ meters at _____ $\mathrm{km}/\mathrm{h}$.

The time taken by the faster train of length $a$ meters running at $x \mathrm{km}/\mathrm{h}$ to pass the slower train of length $b$ meters running at $y \mathrm{km}/\mathrm{h}$ in the same direction. The time taken to cover $(a+b)$ meters in _____ $\mathrm{km}/\mathrm{h}$

If the speed of a boat downstream is $x \mathrm{km}/\mathrm{h}$ and the speed upstream is $y \mathrm{km}/\mathrm{h}$, then its speed in still water is _____ $\mathrm{km}/\mathrm{h}$.

The speed of a boat in still water is $9 \mathrm{km}/\mathrm{h}$ and the speed of the stream is $6 \mathrm{km}/\mathrm{h}$, then the speed of the boat downstream is _____ $\mathrm{km}/\mathrm{h}$.

 If the speed of a boat in still water is $u \mathrm{km}/\mathrm{h}$ and the speed of the stream is $v \mathrm{km}/\mathrm{h}$, then the speed of the boat upstream is _____ $\mathrm{km}/\mathrm{h}$.