difference of two numbers means (x-y)
this difference is nine more than the smaller number
x-y=9+y
x-y-y=9
x-2y=9......[1]
the sum of the two numbers is 54
x+y=54.......[2]
take the two equations together,
x-2y=9
x+y=54
subtract equation [2] from [1]
x-2y-(x+y)=9-54
x-2y-x-y=-45
-3y=-45
3y=45
y=15
x+y=54
x=54-y=54-15=39
x=39,y=15
Hope this helps,
Prabhat