The time $t$ (in hours) required to travel a fixed distance varies inversely as the speed $s$ (in $mi/hr$). If it takes $6$ hours to travel a certain distance at $50mi/hr$, how long will it take to travel the same distance at $75mi/hr$?

If $y$ varies directly as $x$, and $y=18$ when $x=6$, find $y$ when $x=10$.

The distance $d$ a car travels varies directly as the time $t$. If the car travels in $3$ hours, find how far it will travel in $5$ hours.

$p$ varies inversely as $q$, and $p=18$ when $q=9$. If $q=12$, what is the value of $p$?