Hi mohd_int,
GMAT questions are carefully-worded (so that they convey specific information to the reader), but there is some unclear language in this prompt that makes 'translating' it into math equations a bit problematic. Are we meant to assume that there are 6000 TOTAL seats (with some occupied and some NOT occupied) OR that there are 6000 OCCUPIED seats?
In the first option, there are 4 variables (upper occupied, upper not-occupied, lower occupied and lower not-occupied) that sum to 6000 and we can create the equation (lower occupied) = 2(upper occupied).
In the second option, there are 2 variables (upper and lower) that sum to 6000 and we can create the equation (lower) = 2(upper).
GMAT assassins aren't born, they're made,
Rich