help please to find the pattern

[goldenstar]

100,90, ---, 73, 66

answer is 81.

Thanks for your help.

[Guest55]

Look at the gaps between the numbers ...

[goldenstar]

Thanks for your help. Brilliant suggestion, but my brain is not good enough to find the gaps.

[Guest55]

Sorry? Are you saying you cannot subtract?

[goldenstar]

Got it now, thanks for your help. Sometimes thinking too much and complicate things.