The total binding energy of a nucleus is the binding energy per nucleon multiplied by the number of nucleons (protons and neutrons), which is the mass number.

The initial total binding energy of the nucleus is $242 \times 7.6 \, \text{MeV}$.

After the break, each fragment has a total binding energy of $121 \times 8.1 \, \text{MeV}$.

Since there are two such fragments, the final total binding energy is $2 \times 121 \times 8.1 \, \text{MeV}$.

The gain in binding energy is the final total binding energy minus the initial total binding energy. Therefore, the gain in binding energy is:

$2 \times 121 \times 8.1 \, \text{MeV} - 242 \times 7.6 \, \text{MeV} = 1960.2 \, \text{MeV} - 1839.2 \, \text{MeV} = 121 \, \text{MeV}$.

Therefore, the total gain in binding energy is $121 \, \text{MeV}$.