a boat covers a certain distance downstream in 1 hour, while it comes back in $1\frac{1}{2}$ hours. If speed of stream be 3kmph. The speed of boat in still water is

A boat covers same distance in upstream and downstream,

Let it be $\text{'}d\text{'}$ km

Let speed of boat in still water $=x\text{kmph}$

$\begin{array}{ccc}& \text{Up}\text{stream}& \text{Down}\text{stream}\\ \text{Distance}& \text{d}\text{km}& \text{d}\text{km}\\ \text{Speed}& \text{x-3}\text{kmph}& \text{x+3}\text{kmph}\\ \text{Time}& 1\frac{1}{2}\text{hrs=}\frac{3}{2}\text{hr}& \text{1hr}\end{array}$

$\text{Distance=Speed×Time}$

Upstream:

$\text{d=}\left(x-3\right)\frac{3}{2}$

$\left(x-3\right)\frac{3}{2}=x+3$

$\left(x-3\right)3=\left(x+3\right)2$

$3x-9=2x+6$

$3x-2x=6+9$

$x=15\text{kmph}$