Gage skated 1 hr 15 min each day for 5 days and 1 hr 30 min each day for 3 days. How long would he have to skate the ninth day in order to average 85 minutes of skating each day for the entire time?

$\text{(A)}\ \text{1 hr} \qquad \text{(B)}\ \text{1 hr 10 min} \qquad \text{(C)}\ \text{1 hr 20 min} \qquad \text{(D)}\ \text{1 hr 40 min} \qquad \text{(E)}\ \text{2 hr}$
1. First, we need to convert all the given times into minutes for easier calculation.
   - 1 hour 15 minutes = \( 1 \times 60 + 15 = 75 \) minutes.
   - 1 hour 30 minutes = \( 1 \times 60 + 30 = 90 \) minutes.

2. Calculate the total minutes Gage skated over the first 8 days.
   - For the first 5 days: \( 5 \times 75 = 375 \) minutes.
   - For the next 3 days: \( 3 \times 90 = 270 \) minutes.
   - Total for the first 8 days: \( 375 + 270 = 645 \) minutes.

3. Determine the total minutes Gage needs to skate over 9 days to average 85 minutes per day.
   - Total minutes needed: \( 9 \times 85 = 765 \) minutes.

4. Calculate the minutes Gage needs to skate on the ninth day to achieve the average.
   - Minutes needed on the ninth day: \( 765 - 645 = 120 \) minutes.

5. Convert the minutes back into hours and minutes.
   - 120 minutes = 2 hours.

Thus, Gage needs to skate for 2 hours on the ninth day to average 85 minutes of skating each day for the entire time.

The final answer is \( \boxed{2 \text{ hr}} \).