I am trying to see how I can assign a number value (10) to a letter
(X) that is typed into a cell. Everytime I type (X) I want it to
represent the number (10) in any formulas that I want to use it in.
So, if a type (X) in seven cells it should add up to 70. ...

One way is illustrated by the example in the CSV file below.

---------- cut here ----------
X,G,"=10*COUNTIF(A1:B6,""X"")"
G,H,
H,X,
X,V,
V,X,
X,G,