Physics
posted by Hannah .
Using the fact that a 1.0 kg mass weighs 9.8N on the surface of the earth and the radius of the earth is roughly 6.4x10^8m.
calculate the mass of the earth.

Use the weight and mass m to get g = 9.8 m/s^2. Then use
g = G m M/R^2 to get the earth's mass M.
G is the universal gravity constant of Newton. Look it up.