Answer :
x= adults
y=children
x+y=20
x=20-y
18x+12y=324
18(20-y)+12y=324
360-18y+12y=324
-6y=324-360
-6y=-36
y=-36/-6
y=6
x=20-y
x=20-6
x=14
14 adults and 6 children
y=children
x+y=20
x=20-y
18x+12y=324
18(20-y)+12y=324
360-18y+12y=324
-6y=324-360
-6y=-36
y=-36/-6
y=6
x=20-y
x=20-6
x=14
14 adults and 6 children