Question 1137768


let the Mackenzie River length be {{{L}}} and the St Lawrence River length be {{{L[1]}}}

The Mackenzie River is {{{1183km}}} longer than the St Lawrence River.

{{{L=L[1]+1183km}}}....eq.1

 The sum of their lengths is {{{7299km}}}


{{{L+L[1]=7299km}}}........substitute {{{L}}} from eq.1

{{{L[1]+1183km+L[1]=7299km}}}

{{{2L[1]=7299km-1183km}}}

{{{2L[1]=6116km}}}

{{{L[1]=6116km/2}}}

{{{L[1]=3058km}}}


now go to eq.1 


{{{L=L[1]+1183km}}}....eq.1, substitute {{{L[1]}}}

{{{L=3058km+1183km}}}

{{{L=4241km}}}


so, the  Mackenzie River is  {{{4241km}}} long, and the St Lawrence River is {{{3058km}}} long