Answer :
220=A+S (adult plus student)
s=220-a
2.50a+1.50s=465
1.50s=-2.50a+465
s=-1.67a+310
then set those equal to each other
220-a=-1.67a+310
220=-.67a+310
-90=-.67a
.67a=90
a=60
then put a back into the first equation
220=S+A
220=s+60
s=160
a=60, s=160
s=220-a
2.50a+1.50s=465
1.50s=-2.50a+465
s=-1.67a+310
then set those equal to each other
220-a=-1.67a+310
220=-.67a+310
-90=-.67a
.67a=90
a=60
then put a back into the first equation
220=S+A
220=s+60
s=160
a=60, s=160