Question 1053598
Use variables not names.
1.{{{Z=2A+5}}}
2.{{{L=A+Z/3}}}
3.{{{Z+L+A=100}}}
Substituting 1 and 2 into eq. 3,
{{{2A+5+A+(2A+5)/3+A=100}}}
Multiply both sides by 3,
{{{6A+15+3A+2A+5+3A=300}}}
{{{14A=280}}}
{{{A=20}}}
Now use equations 1 and 3 to solve for Z and L.