Question 779148
small s
medium m
big b


{{{s+m+b=16}}}.
{{{b=s+m}}}.
{{{3s=1+b}}}.


Solution can be done in more than two ways.  Easiest start might be, solve the last equation for b and substitute into the second equation.  Solve the second equation either for s or for m.  


You might want to arrange the system this way:
{{{highlight(s+m+b=16)}}}
{{{highlight(s+m-b=0)}}}
{{{highlight(3s+0*m-b=0)}}}
Which suggests a quick way to find b using the first two equations.