Hi, Michael. You should take airport bus to the city center of Chengdu and then change taxi to Huajuesi Bus Station or North Bus Station to find the buses to Mianyang. You will get to Mianyang some 1.5 hours later. Fucheng is a ditrcit, you should ask the restaurant or specific place that your are going to and show it to the taxi driver when you get off the bus at Mianyang.