How can I solve these problems?

3. Scientists uncover that an unknown substance only has 20% % of its original mass left after 30 days. What is the half life of this unknown substance?6. Calculate the energy released in MeV of the following reaction. 12C + 1H+- 13N a) Is this a fission or fusion? Explain your reasoning. Richard, H b) Calculate the energy released in MeV, given that: mc-12 = 12.000000 u, my-1 = 1.007825 u, mN-13 = 13.0057386u 1 u = 1.66 x10-27kg, 1MeV =1.602 x 10-3J c=3.00 x108 m/s