Question 1116244
m, Mary
b, Brother
c, Cousin

{{{system(m=b+7,b=c-10,m+b+c=47)}}}


The first and second equations can be written in terms of b; and then these used to rewrite the last equation all in ONE variable.



{{{system(m=b+7,c=b+10)}}}


The age sum equation:  {{{(b+7)+b+(b+10)=47}}}
Solve and use it to evaluate m and c.