Three sell orders are placed for a stock today. Listed below are the bid and ask quotes at various times:

Time	Bid Price	Bid Size	Ask Price	Ask Size
10:00 AM	$12.10	300	$12.16	400
1:00 PM	$12.00	300	$12.07	400
2:00 PM	$11.80	300	$11.88	400

The following trades take place:

a. At 10:00 AM, the trader placed an order to sell 100 shares. The execution price was $12.11.

b. At 1:00 PM, the trader placed an order to sell 300 shares. The execution price was $12.00.

c. At 2:00 PM, the trader placed an order to sell 600 shares. The average execution price was $11.75.

Calculate the quoted and effective spreads for each of these orders. 

Calculate the average quoted and average effective spread.