Question 595771
rH=5.5
rD=7.5
x= number of hours

{{{(x/5.5)+(x/7.5)=1}}}
{{{(x/(11/2))+(x/(15/2))=1}}}
ex. {{{x/(1/2)}}} = {{{2x}}}
{{{((2/11)x)+((2/15)x)=1}}}
Find Common Denominator
{{{((30/165)x)+((22/165)x)=1}}}
{{{(52/165)x=1}}}
{{{52x=165}}}}
{{{x=165/52}}}
or 
x=3.17 hours or 3hours and 10min