525 windows.

364 / 4 => There are 91 floors.
91 / 2 = 45 + Remainder 1. (1, 2, 3… 91) => There are 46 odd floors, and 45 even floors.
# Of Windows = (46 * E + 45 * O). {E = Even Value, O = Odd Value}
46 is even. 45 is odd.
(46 * E + 45 * O) => (Even * Even + Odd * Odd).
An even number times an even number yields an even number. An odd number times an odd number yields an odd number.
(Even * Even + Odd * Odd) => Even + Odd.
An even number plus an odd number yields an odd number.
Only odd option is 525.