Objective: How can you measure something to see if it is about 6 inches long without a ruler?

Which of the following solutions is more sound in terms of naive physics reasoning?

Options: a. Place a Dollar (Or other American Bill) beside the item. A bill is about 6 inches - 2 of them is about a foot.. b. Place a quarter (Or other American coin) beside the item. A coin is about 6 inches - 2 of them is about a foot..
a.