If Lauren and Jon bought 50 acres how many Hectares did they buy if 1 acre = .405 Hectares?

Question

20.25 Hectares

Using the above question and answer how many square miles is their land if 1 mi^2 = 640 acres?

How would I set this part up

Answer 1

50/640 = x/1

640x = 50

x = 0.0312 square miles

Answer 2

How did you get x?

Answer 3

This reads as
50 acres is to 640 acres as unknown is to 1 square mile.

X = unknown.

640x = 50

Divide both sides by 640.