First, you add the two parts of the ratio together. 8+5=13. Then you do 390 divided by 13 which is 30. After this, you multiply 30 by each side to get the ratio to be equal. 30x8=240, and 30x5=150. This can now be put into the ratio 240:150. As you said it was in the ratio adults to children, it must stay in that order. The part of the ratio for children is 150.
The answer to your question is 150. You can double-check your answer by adding up the two parts again. 240=150=390 so you can be assured that your answer is truly correct. Thank you for uploading this question. I hope my explanation was helpful enough for you
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