So let's name the numbers x and y.
we know that their sum, x+y is
and that that their difference, x-y is
so, from the last one we can find out x:
x-y=
x=+y
we can substitute this into the first one:
+y+y =
+2y =
2y=
(7-2=5, but you have to "borrow" one because the fraction of the number from which you substract is smaller than of the other number)
so y=
then x will be
x=+
x=
we know that their sum, x+y is
and that that their difference, x-y is
so, from the last one we can find out x:
x-y=
x=
we can substitute this into the first one:
2y=
so y=
then x will be
x=
x=
