Question 1114386
{{{system(x+y=180,y/x=5/3)}}}  but not the only way to start.


ONE VARIABLE SOLUTION
Angles are 3n and 5n.
{{{3n+5n=180}}}
{{{8n=180}}}
{{{n=22.5}}}


The angles are  67.5 and 112.5 degrees each.