Hints:

• The total of the numbers in each circle is the same. Try adding all four circles together.

• When you sum all four circles, you get the total of all the numbers (36) plus the four overlap regions (since each shared number is counted more than once).

• Therefore, each individual circle adds up to:
  $\text{Total of all numbers (36)}+\text{Sum of overlaps}÷4$
  That is: 9 + (Overlap Sum ÷ 4)

• The smallest possible overlap sum is: 1 + 2 + 3 + 4 = 10
  The largest is: 5 + 6 + 7 + 8 = 26
  But it must be divisible by 4. So the valid overlap sums are:
  12, 16, 20, or 24

• That means each circle’s total could be:
  9 + 3 = 12,
  9 + 4 = 13,
  9 + 5 = 14, or
  9 + 6 = 15

• This narrows down the possibilities and gives you a solid place to start!