5 6 6 9 ( ) 90 There is some logic between the numbers above. Please fill in the numbers in brackets

5 6 6 9 ( ) 90 There is some logic between the numbers above. Please fill in the numbers in brackets

eighteen
Rule: (first term-3) × (second term-3) = third term
6=(5-3)x(6-3)
9=(6-3)x(6-3)
18=(6-3)x(9-3)
90=(9-3)x(18-3)