The isotope cobalt-60 has a nuclear mass of 59.933820 u
calculate the mass defect of cobalt-60 using the following information.
mass of proton: 1.007825 u
mass of neutron: 1.008665 u
1 u = 931.5 mev

Using the Einstein relationship: 

Nuclear binding energy = Δmc^2 

number of protons x 1.007825 x 931.5 Me V = X 

number of neutrons x 1.008665 x 931.5 Me V = Y 

Adding up these energies = X + Y 

59.933820 x 931.5 Me V = Z 

Subtract Z from (X+Y)

(X+Y) -Z = Nuclear binding energy 

Divide by the total number of nucleons by the sum of all protons and neutrons in Co 60

(524.807 Me V)/(60 nucleons) = 8.74678 Me V/nucleon.

Distance^2= yellow line ^2 (see picture) = 30^2 + 49^2so distance = squareroot of (300^2 +49^2)i dont know if this is how to solve it, but i cnt think of another way