The sum of two numbers is 13. If one number is subtracted from the other, the result is - 3. Find the number

Let a>b

a+b=13 and b-a=-3 solve the first for b

b=13-a and use this b in the second equation ...

(13-a) - a=-3

13-2a=-3

-2a=-16

a=8, and since b=13-a,

b=5

b+a=13, 5+8=13, 13=13

b-a=-3, 5-8=-3, - 3=-3

5, 8. The two numbers are '5', and '8'. 5+8=13, while 5-8 = - 3.