The median is the middle value. Find out how many you have in the table, and then where the middle one should be.
The mean is where you add up all the numbers and then divide by how many you have. With grouped frequency tables you need to assume that all the data are equal to the mid-point of their catagory.
The mode is the most popular. You can just state the most popular group here I believe, as you have no idea which of the numbers is the most popular.