Answer:
Hello!!! Princess Sakura here ^^
Explanation:
If the lower level has 100 less than 2 times as many seats as the upper level then the expression is 2x-100 and the middle level has 80 more than 3 times as many seats as the upper level so it's 3x+80 and lastly the top level is just x.
so now for the equation you would add all those expressions and they all should equal 2680:

but now don't forget to plug in for the middle level:

Therefore the middle level has 1430 seats.