Finish the solution using the equation shown by the other tutor.
Then notice that the formal algebraic solution follows exactly the same path as this solution that uses only logical reasoning and a bit of mental arithmetic:
(1) Since the larger number is 11 more than the smaller, subtract 11 from it.
(2) Now the two numbers are the same; and their sum is 39-11 = 28.
(3) So each of the numbers is 28/2 = 14.
(4) Now add the 11 back on to the larger number; the two numbers are 14 and 14+11 = 25.