From a search "To remove PMI, or private mortgage insurance, you must have at least 20% equity in the home. You may ask the lender to cancel PMI when you have paid down the mortgage balance to 80% of the home's original appraised value. When the balance drops to 78%, the mortgage servicer is required to eliminate PMI."
So, if you're at 78% with a new appraisal, you're all set.