The sentence is “The difference between number and 12 is 54”.

Let n be the number.

The word difference indicates subtraction, and the symbol is .

Thus, the numerical expression is “”.

The equation is .

Apply addition property of equality: Add 12 to each side.

                                (Apply additive inverse property: )

                                      (Apply additive identity property: )

                                              (Add: )

The value of the expression is 66.