Hi Thomas.

Here's how I'd do a similar question backwards:

Say you have two numbers, 450 and 350. The difference is 100 and the total is 800. The midpoint (average) of these two numbers has to be the first number and the second number has to be the the difference between the total and the first number.

So going forwards,

(100 + 800) / 2 = 900 / 2 = 450 (the first number)

and

800 - 450 (the total minus the first number) = 350, the second number.

Now you try it with your numbers.
Stephen La Rocque.