At different times on a certain day, a manager at a theme park recorded the number of visitors. An exponential model gives the estimated number of visitors,

, at the theme park

hours after the theme park opened, where

. Based on the model, 85 visitors were estimated to be at the theme park when it opened, and every 30 minutes the estimated number of visitors increased by 140% of the estimated number of visitors 30 minutes earlier. Which of the following equations best represents this model?