Maria is in the state park riding her bike on the new bike trail. she starts at the beginning of the trail and bikes for 4 miles. after the first 4 miles, her friend aiden joins her and they ride the rest of the trail. by the end of the trail, maria has been riding for two and half hours, while aiden has been biking for two hours. assuming they are both riding their bikes at a constant speed the entire time, how long is the bike trail?