Question 991678

let's girl's age be {{{g}}} and boy's age {{{b}}}
if a girl is {{{3}}} years older than her brother, then we know that

{{{g=b+3}}}.......eq.1

if their combined age is {{{35}}} years, we know that 

{{{g+b=35}}}........eq.2...substitute {{{b+3}}} for {{{g}}}

{{{b+3+b=35}}}

{{{2b=35-3}}}

{{{2b=32}}}

{{{b=32/2}}}

{{{b=16}}}=> boy's age


{{{g=b+3}}}=>{{{g=16+3}}}=>{{{g=19}}}=>girl's age