Hey! :)
Let us make these number be x and y.
x + y = 54
x - y = 26
Now, add these equations to get the following:
2x = 54 + 26 = 80
2x = 80
x = 80/2 = 40
Now, x + y = 54 meaning 40 + y = 54.
Therefore y = 54 - 40 = 14.
Have a great rest of your day :)
