What is a placard letter

A placecard letter is a notice post in a public place to to inform information on something.  

Explanation:

These are the answers to the three questions and their explanations:

1. From the Georgia colony, the city that would have experienced the most commerce during colonial times was Savannah, this is because Savannah´s location at the mouth of a river, and near the ocean, was easier to be accessed than other cities.

2. The car´s origins can be dated to as early as the 1700´s, most precisely, 1769. However, it became MOST popular in the 20th century, when Henry Ford started the mass production of the Ford Model T series, in 1913. It was the first time that cars were sold in such high numbers.

3. The mode of transport that would be LEAST used when trading large goods would be the aircraft as it is one of the most expensive modes of transport and it cannot hold as much cargo as a ship, or a train can, and it is much more expensive than a truck.