On Saturday's lunch rush at Ada's diner, they sold 237 sandwiches.Of those sandwiches sold:

• 74 sandwiches included turkey
• 53 sandwiches included cheese
• 18 sandwiches included both turkey and cheese
• 6 sandwiches included turkey and sprouts
• 6 sandwiches included both cheese and sprouts
• 3 sandwiches included all three ingredients
• 6 sandwiches had none of these ingredients (turkey, cheese, or sprouts)

How many sandwiches only included sprouts (of these three ingredients)?