Sum of two numbers is 24 and the difference is 15.what are the two numbers ?

Let,
the bigger number  be "x"
the smaller number be "y"
Now, according to the question,
x + y = 24equation (1)because the sum of numbers is 24
x - y = 15 equation (2)because their difference is 15

Taking equation (2),
x - y = 15
x = 15 + y equation (3)

Now, Taking equation (1)
x + y = 24
(Substituting the value of "x" form equation (3) we get)
15 + y + y = 24
(Subtracting 15 on both sides, we get)
y + y = 24 - 15
2y = 9
y = 9 / 2
y = 4.5
Now, 
Taking equation (3)
x = 15 + y
(Substituting the value of y , we get)
x = 15 + 4.5
x = 19.5

So, the two numbers are 19.5 and 4.5

Chope you get it right gl