How an auto insurance 90/10 responsibility works?

What’s the least expensive insurance carrier to get a 21-year old using a 2000 ford mustang?

Im 17 and i reside with my grandma but idrive along with his insurance. I changed the businesses because of a fee increase now I was given a medical form for my doctor to signal that claims hes okay to travel by them. I told the physician I would like him to signal it since I-drive the automobile not my grandmother but he wont sign it what do I-do i really require it. The physician mentioned he gets dizzy spells but i need asap to be driven by it and my grandpa cant push because hes 80

“funny. Each time i notice a clumsy /reckless driver”I had been just wondering if anybody out-there had guidance for insurance great motor insurance charges