The explanation seems fine to me. Or should a competent moderator step in and interpret?
amira01, there's little doubt that your washing machine waste combines with the waste from your kitchen sink, and that you have a partial blockage after the point where they combine.
It's also possible that you have a blocked gully outside (if you have a gully).
The cheapest and easiest thing to try first would be a proprietary cleaner. If you want a suggestion then I would use this one:
Wait until all water has drained away before trying that option. If it doesn't work then you'll have to take the trap off, and whatever part of the waste comes apart, and clean the pipes manually.
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