Explanation:
Let the two numbers be x and y
By the question
x + y = 87 ..... equation (I)
x - y = 65 ...... equation (II)
Now adding both equations we get
2x = 152
x = 152 / 2
Therefore x = 76
Putting x = 76 in equation i
76 + y = 87
y = 87 - 76
Therefore y = 11
The two numbers are 76 and 11.
Hope it helps :)