Question 1084586
x, children
y, adults

{{{6x+15y=231}}}

{{{2x+5y=77}}} or  {{{y=-(2/5)x+77/5}}} or  {{{y=(77-2x)/5}}}.


More than one solution possible.  Look for any whole number solution combinations.  x=11 and y=11 will work.  


A possible solution among others:
11 students 
and 
11 adults