Two identical isolated particles, each of mass 1.55 kg, are separated by a distance of 30.6 cm. What is the magnitude of the gravitational force exerted by one particle on the other?

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I solved it as:
Fg = G(m^2/r2) = G(m/r)2

= 6.673x10^−11 Nm2/kg2 (1.55 kg/30.6 m)^2 = 1.14X10^-7

Which is the wrong answer D:

30.6 cm seems to have become 30.6 m instead of .306 m. Does this solve your problem?