Answer
See explanation.
Work Step by Step
a. Charge and the number of nucleons are conserved. The new Z is 14 - 12 = 2. The new A is 28 - 24 = 4.
b. Calculate the mass change in the reaction. The nuclide X is helium-4. Use the atomic masses given to calculate the mass defect of $-0.01072u$, the total masses on the left minus the total masses on the right. The negative sign means there is more mass afterward than before.
This equals a minimum energy of 9.98 MeV of energy that was provided by the photon.
