If you subtract 12
from my number and
multiply the difference by -3,
the result is -54.

the answer is 30

Step-by-step explanation:

Let the number be x

- 3 (x - 12) = - 54

-3x + 36 = -54

-3x = -54 - 36

-3x = -90

x = -90/-3

x = 30