Ineed to know how to balance the scales it says ''make the scales balance by using addition and subtraction to find in the missing numbers.

This would be much, much, much easier if you told us
what numbers you do have on each side of the scale now.

The idea (probably) is that the scale is balanced when
the numbers add up to the same amount on both sides.

So you need to put some numbers in the blanks that will either
add more to the side that has less, or subtract some from the side
that has more, to make both sides equal.