Question

Help with the question I know this question is simple but i am weak in physics
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Answer 1

F = G M1 M2 / R^2

R^2 = G M1 M2 / F

R^2 = 6.67 E-11 * 6.78 E26 * 5.42 E20 / 8.6 E10

R^2 = 6.67 * 6.78 * 5.42 / 8.6 * E25

R^2 = 28.5 * E25 = 2.85 * E26

R = 1.69 E13 m