Question 128200
Call the number of upper tickets = u

Since the total number of seats is 16400, the number of lower level musr be 16400-u

So 5.5u + 16.3(16400-u) = 183080

5.5u -16.3u + 267320 = 183080

10.8u = 84240

So u (upper seats) = 7800

And hence the number of lower seats is 8600.