The number of miles my car can go on a gallon of gasoline is normally distributed with a mean of 30 miles and a standard deviation of 4 miles.

1. I currently have exactly one gallon in my tank, and have to travel 35 miles to my destination. What is the probability I make it to my destination before I run out of gas?
2. Find the distance D so that I have a 90% chance of traveling D miles before running out of gas (assuming again that I start with one gallon).
3. Suppose I can change my mean mileage per gallon by adjusting the carburetor. What value should I set the mean to so that I have a 90% chance of making it 35 miles on one gallon of gas?