Question 747824
Call the original unburned length for each candle, 1 unit.
Also note that rate*time is the amount of length burned.
<pre>
                        rate           time           length remain 

first candle             1/5            x              1-(1/5)x

second candle            1/4            x              1-(1/4)x
</pre>
"find the time, in hours, taken for the height of the first candle 
to be four time that of the second candle ."


That should mean,  {{{1-x/5=4(1-x/4)}}}.


To solve that,
{{{1-x/5=4-x}}}
{{{5-x=20-5x}}}
{{{-x=15-5x}}}
{{{4x=15}}}
{{{x=15/4}}}
{{{x=3&3/4}}}----------hours