Assigning numerical values to characters

I am required to assign a numerical value to a character such as 'a' = 2.5,and 'xl' = 2.5x2.5 ft. I am unsure of how to assign a numerical value to characters. Below is an example of what i have to complete.

-A separation of “A” or “a” means 2.5 foot distance between moshers -A mosher size of ”L” or “l” means each mosher takes up a 1.5 foot by 1.5 foot space

For the first point I am supposed to use a char variable type and for the second a string data type.