9. (10 points) In "The Martian," Mark unfortunately did not follow the other 5 astronauts back to Earth and was left alone on Mars. Mark must find a way to survive and wait for rescue. The habitat module left has 5 days of food for each astronaut and 50 kilograms of non-drinking water. There is also a large enough garden, which Mark plans to use for growing potatoes. After 30 days, 2.5 kilograms of potatoes can be harvested per square meter, but it requires 4 kilograms of water for irrigation. Mark needs to eat 1.875 kilograms of potatoes per day to survive. How many days can the food and potatoes support Mark at most?
【Analysis】First, based on how many days one can survive without potatoes, then calculate the total amount of potatoes based on the water storage, and divide by the amount of potatoes consumed daily to get the number of days.

【Solution】Solution: The food reserve for 6 people can sustain one person for $5 \times 6=30$ days. The non-drinking water storage is $50 \times 6=300$ kg.

The total amount of potatoes that can be harvested is $300 \div 4 \times 2.5=187.5$ (kg).
The total number of days that can be survived is $187.5 \div 1.875=100$ (days).
$$
100+30=130 \text { (days) }
$$

Answer: Mark can survive for 130 days.