Question 851617
{{{A+B=117}}}
{{{A-B=21}}}
Add the equations,
{{{A+B+A-B=117+21}}}
{{{2A=138}}}
{{{A=69}}}
Now use either equation to solve for {{{B}}}
{{{B=117-A}}}
{{{B=117-69}}}
{{{B=48}}}