How much is a 1916 w mercury dime worth?

The mintmark is on the reverse of the coin and all Mercury Head dimes have the "W" on the front of the coin it's the designers initial, Adolph A. Weinman. 1916 is the first year of issue and it's very important to check the back of the coin for a mintmark, if it has one it can only be a "S" or "D", the "D" mintmark is the key-date of the series and the coins are very valuable. Take it to a coin dealer or collector for a better idea of value.