Answer :
4x + 6y = 2340
x + y = 450 --> y = 450 - x
4x + 6(450 - x) = 2340
4x + 2700 - 6x = 2340
-2x = -360
x = 180 --> there were 180 $4 tickets sold.
and
450 - 180 = 270 $6 tickets
x + y = 450 --> y = 450 - x
4x + 6(450 - x) = 2340
4x + 2700 - 6x = 2340
-2x = -360
x = 180 --> there were 180 $4 tickets sold.
and
450 - 180 = 270 $6 tickets