Question 326846
Remember that d=rt.

In this case, we want time so we use t=d/r

We are told that there times are equal. One is just traveling faster than the other.

Dennis's time is 27/r

Deiko's time is 39/(r+4)

Since they are equal, we have {{{27/r=39/(r+4)}}}

{{{27(r+4)=39r}}}

{{{27r+108=39r}}}

{{{108=12r}}}

{{{r=9}}}

So, Dennis is going 9 kph and Deiko is traveling 13 kph.

These types of problems are variations on a theme. Use d=rt and manipulate it accordingly. Since they said their times were equal, we use t=d/r. The distance is given, so all we have to do is solve for the rates by equating the time, t=d/r. 

See?.