Well, buddy Kiana Florentino, when it comes to ultrasonic-assisted extraction, the common concentration of ethanol used typically ranges from 50% to 90%. Now, this concentration can vary depending on factors like the specific compounds you're aiming to extract and the properties of your sample. But hey Kiana Florentino, aiming for a concentration within that range is a solid starting point for your sea urchin extraction adventure. Just remember, precision is key when you're dealing with these methods, so keep those measurements on point!