Answer:
c = 53 miles
Step-by-step explanation:
Answer:

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Work Shown:

You could expand terms out and simplify, but I think it's more handy to leave it in this form so you can easily spot the center and radius from a glance.
1. 30
2. 40
3. 70
4. 200
5. 220
6. 300
7. 8,100
8. 120
9.650
10. 2,200
11.6,000
12. 7,000
13. 1,560,000
14.1,000