An 80kg astronaut has a weight of 120N. How many radii above the earth is he?

80 * 9.81 = 785 N at Rearth from center

120/785 = rearth^2/R^2

R^2 /Rearth^2 = 6.54
R/Reath = 2.56
so
2.56 Rearth - 1 Rearth = 1.56 Rearths above surface