$A$ motor boat whose speed is $18\, km/h$ in still water takes $1\, hour$ more to go $24\, km$ upstream than to return downstream to the same spot. Find the speed of the stream. (in $ km/h$)

Two water taps together can fill a tank in $9 \frac{3}{8}$ hours. The tap of larger diameter takes $10 \text{ hours}$ less than the smaller one to fill the tank separately. Find the time in which each tap can separately fill the tank.

The sum of the reciprocals of Rehman's ages,(in $years$) $3$ years ago and $5$ years from now is $\frac{1}{3}$. Find his present age. (in $years$)

Find the values of $k$ for the following quadratic equation,so that it has two equal roots:
$2 x^{2}+k x+3=0$

Find the roots of the following quadratic equation,if they exist,by the method of completing the square: $2x^{2} + x + 4 = 0$.

Find the nature of the roots of the following quadratic equation. If the real roots exist,find them:
$2x^2 - 6x + 3 = 0$