let L represent lower level tickets and U upper level.
Starter equations:
L + U = 2368
78L + 59U = 157800
Solve simultaneous equations:
59L + 59U = 139712
so 19L = 18088
L = 952
U = 2368 - 952 = 1416
952 lower level tickets and 1416 upper level tickets were sold.