The rule is: the sum of the number of inner circles and outer circles in the previous circle+the number of outer circles in the next circle = the sum of the number of inner circles and outer circles in the next circle.

10-( 1+2+6)+8=20-( 1+2+8)

20-( 1+2+8)+5=28-( 1+5+8)

28-( 1+5+8)+7 = X-(5+4+7) so X = 37.

37-(5+4+7)+5 = 87-(5+7+y) so y = 49.

You got it?

That is, the fourth circle is filled with 37.

Fill in 49 in the blank outside the fifth circle.