We can take the number of apartment buildings to be ‘x’ and work it out from there. Here, let us see another approach where we assume the number to be 100. The below figure would help us work out with that approach:
We see above that the number of single bedroom without balcony comes out to be 14 when total number of apartments is assumed to be 100. Since, the actual number of single bedrooms without balcony is 28 ( 2 times 14), the total number of apartments must be 2 times 100 or 200.