Hey there :)
Let us translate the words into mathematics!
The difference of 2 numbers is 3
x - y = 3
The sum of 2 numbers is 13
x + y = 13
(eq. 1) x - y = 3
(eq.2) x + y = 13
eq. 1 + eq.2 ⇒ x - y = 3
+ x + y = 13 ( -y and +y cancels out )
2x = 16
[tex] \frac{2x}{2} = \frac{16}{2} [/tex]
x = 8
We have the value of x, simply substitute it in either of the formulae to find y
x - y = 3 , 8 - y = 3 , 8 - 3 = y , 5 = y
x + y = 13 , 13 - 8 = y , 5 = y
x = 8 , y = 5
