Are you sure about the model number? I see several 30CC engine string trimmers by Ryobi. Two are the Ryobi RY30040B (SS30) and a RY30544 (SS30).
For both of these models, mix a high quality 2-cycle engine oil at 2.6 oz. per gallon of gasoline to pour into the gas tank. This ratio is used in several other Ryobi string trimmer models. Many Ryobi product manuals are available here:
https://www.ryobitools.com/power-tools/support/manuals . Most Ryobi gas powered and 40V battery-powered tools will have a model number that starts with RY. The 18 V battery powered models often start with a P.
I hope this helps. If you add a comment with the actual model number, I may be able to provide more information.
Cindy Wells
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