Puzzle ZPSD 

Workings

Hint
Find the weight of the bottle first.

Answer
24 ounces.

The bottle weighs 16 ounces.

Reasoning
As a bottle (B) weighs eight ounces plus half a bottle, we can write this as:
   B = 8 + ¹/₂ x B
  ¹/₂ x B = 8
   B = 16

As the bottle weighs 16 ounces, a bottle and a half weighs 16 + 8 = 24 ounces.