according to question ,
let two number be x and y
1 case,
x+y=18...................1
2 case
x-y=8
x=y+8 ................2
putting valu of x in eq 1 from eq 2
y+y+8=18
2y=18-8
2y=10
y=5
putting value of y=5 in eq 2
x=8+5
x=13
therefore, the number are 5 and 13