Uranium-235: 200 MeV per fission
Uranium-233: 197 MeV per fission
Plutonium-239: 210 MeV per fission

The amount of energy needed to reach 15,111 megatons is:
E = 15.111 × 10^6 × 4.184 × 10^12 Joules, where 4.184 × 10^12 Joules
is the conversion of 1 megaton to Joules.

Now we can calculate the number of fissions needed to
each element, considering the efficiency of 0.147:

For Uranium-235:
N_fissions_Uranium-235 = E / (Efficiency × Energy per fission)
N_fissions_Uranium-235 = 15.111 × 10^6 × 4.184 × 10^12 / (0.147 × 200)
N_fissions_Uranium-235 ≈ 5,351 × 10^17 fissions

For Uranium-233:
N_fissions_Uranium-233 = E / (Efficiency × Energy per fission)
N_fissions_Uranium-233 = 15.111 × 10^6 × 4.184 × 10^12 / (0.147 × 197)
N_fissions_Uranium-233 ≈ 5,442 × 10^17 fissions

For Plutonium-239:
N_fissions_Plutonium-239 = E / (Efficiency × Energy per fission)
N_fissions_Plutonium-239 = 15.111 × 10^6 × 4.184 × 10^12 / (0.147 × 210)
N_fissions_Plutonium-239 ≈ 5057 × 10^17 fissions

Finally, we can calculate the amount of mass of each element needed,
considering the number of fissions and the molar mass of each element:

For Uranium-235:
m_Uranium-235 = N_fissions_Uranium-235 × Molar mass of Uranium-235 / Avogadro's number

The molar mass of Uranium-235 is approximately 235 g/mol.

For Uranium-233:
m_Uranium-233 = N_fissions_Uranium-233 × Molar mass of Uranium-233 / Avogadro's number

The molar mass of Uranium-233 is approximately 233 g/mol.

For Plutonium-239:
m_Plutonium-239 = N_fissions_Plutonium-239 × Molar Mass of Plutonium-239 / Avogadro's Number

The molar mass of Plutonium-239 is approximately 239 g/mol.

Now we can calculate the masses:

For Uranium-235:
m_Uranium-235 = 5.351 × 10^17 × 235 / 6.022 × 10^23
m_Uranium-235 ≈ 21.04 kg

For Uranium-233:
m_Uranium-233 = 5.442 × 10^17 × 233 / 6.022 × 10^23
m_Uranium-233 ≈ 21.43 kg

For Plutonium-239:
m_Plutonium-239 = 5.057 × 10^17 × 239 / 6.022 × 10^23
m_Plutonium-239 ≈ 19.97

Now we can calculate the required masses of each element
to reach 15,111 megatons of energy:

For Uranium-235:
m_Uranium-235 = 5.351 × 10^17 × 235 / 6.022 × 10^23
m_Uranium-235 ≈ 21.04 kg

For Uranium-233:
m_Uranium-233 = 5.442 × 10^17 × 233 / 6.022 × 10^23
m_Uranium-233 ≈ 21.43 kg

For Plutonium-239:
m_Plutonium-239 = 5.057 × 10^17 × 239 / 6.022 × 10^23
m_Plutonium-239 ≈ 19.97 kg

Therefore, to reach 15,111 megatons of energy,
It would take approximately:

     21.04 kg of Uranium-235
     21.43 kg of Uranium-233
     19.97 kg of Plutonium-239