Question 1054784
1.{{{H=B/3}}}
2.{{{T=H+B}}}
3.{{{H+B+T=40}}}
Substituting,
{{{(T)+T=40}}}
{{{2T=40}}}
{{{T=20}}}{{{cm}}}
Then,
{{{H+B=20}}}
Substitute eq. 1,
{{{H+3H=20}}}
{{{4H=20}}}
{{{H=5}}{{{cm}}}
and 
{{{B=3(5)}}}
{{{B=15}}}{{{cm}}}