Let the two numbers be x and y.
The difference between the numbers is 4. Therefore
x - y = 4 (1)
The sum of one-half of each number is 18, therefore
x/2 + y/ 2 = 18
x + y = 36 (2)
Add equations (1) and (2).
(x - y) + (x + y) = 4 + 36
2x = 40
x = 20
From (2), obtain
y = 36 - x = 36 - 20 = 16.
Answer: The two numbers are 16 and 20.