Caculate the number in the middle of 12 and 17

Aformual for 8 bottles of window cleaner calls for 6 cups of rubbing to customers alcohol 2 1/4 gallons of water and 1 1/2 cups of ammonia alcohol would the forula call if a factory made 1,280 bottles for stores to sell to customers

Can anyone me with 32,33,36,37,and 40.

The jewelry store is having a sale. necklaces that were regularly priced at $23.50 are on sale for $18.80. what is the percentage of decrease in the price of necklaces?