The sum of two numbers is 54 . the smaller number is 12 less than the larger number. what are the numbers?

Let x=one number and x+12= the other number.  Together the numbers=54.  Set up the equation:  x+x+12=54;  Combine the variables;  2x+12=54;  Subtract 12 from both sides of the equation;  2x=42; Divide both sides of the equation by 2;  x=21 is one number and 21+12=33 is the other number.  Check:  2(21) +12=54;  42+12=54;  54=54.