First, take out the whole number portion, and solve the decimal part, which is 0.85. 0.85 = 85/100. So, the mixed number would be 2 85/100. However, most teachers want you to simplify your mixed numbers, so divide both numbers by a factor that you think is common. 5 is a common factor, so 85/5 = 17. 100/5 = 20. So, the answer is simplified to 2 17/20.
Hope that helped.