Astronomers are proud of their telescopes, and often say they can "resolve a dime at so many miles." How many miles can you move a disk (D = 6.

Astronomers are proud of their telescopes, and often say they can "resolve a dime at so many miles." How many miles can you move a disk (D = 6.0 cm) from a 325-cm-diameter telescope mirror and just resolve it using light of wavelength 785 nm?

We know the answer is 61 mi, but we have no idea how to get there, any help would be greatly appreciated.