Answer:
The first number is 20, the second one is 11
Explanation:
Let the first number be x and the second number be y
Since it says "9 is the difference between two numbers", the first equation will be x-y=9
It also says that "their sum is 31". That means the second equation will be x+y=31
here are the two equations:
x-y=9
x+y=31
You can solve this any way you like, but I'll show elimination
add the two equations
x-y=9
x+y=31
2x=40
divide by 2
x=20
Substitute 20 as x in one of the equations
20+y=31
subtract 20 from both sides
y=11
That means the two numbers are 20 and 11
Hope this helps!