How do you tell what number letters are?

Answer 1

It depends on the situation.

Sometimes we have an equation like:

X - 14 = 7, in which we can solve for the letter (in this case, X, which equals 21).

Sometimes they are intended to be variables:

Y = X3-17X + 4, where the letters may be many numbers, but are restricted when other variables are known.

Other times, letters refer to specific constants:

e = approximately 2.718281828.

pi = approximately 3.141592654.

i = sqrt(-1) and is imaginary.