6) The Half life of a radioactive substance is 30 years and you start with 3mg of substance. How much is present after 96 years? 7) Your car needs repairs, and the cost is as follows, there is a fixed $250 for parts and $75 per hour for labor. (a) How much will it cost if your car takes 18 hours to repair? (b) Write a linear function that describes the situation. Clearly identify all variables used? (c) If you paid $700 to fix the car, how many hours of work did they perform on the vehicle?