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The opening in the middle can be done with a Pocket based on a sketch. When you make the sketch, all the curves need to be constrained to the outside geometry and/or the holes. You could use the Offset tool, or you could just draw new arcs and circles and constrain them concentric to their outside partner. Either method will require a lot of trimming - maybe that's where you failed? Use the Sketch Analysis tool to check for a 'Closed Profile'