Please help me answer the following problem:

Problem 7 (25 points) J Light is incident on the surface of metallic sodium, from which 2.4 ev are required to remove an electron. The stopping potential is 6.4 volts. (Note that 1 eV = 1.6 x 10-19 J.) (a) Find the wavelength of the incident light. (8 points) (b) Would this light emit any electrons from a metal whose work function is 7.3 ev? If so, determine the maximum kinetic energy of an emitted electron (in either J or ev). If not, explain why. (8 points) (c) If the power of the light source is 5.0 mW, how many photons are emitted by the source in 20 seconds, and what is the momentum of each photon? (9 points)Problem 8 (20 points) The radioisotope Sr has a half-life of 29 years. One sample has an initial activity of 8.90 x 105 Bq. (Note that the mass of one proton or neutron is approximately 1.67 x 10-27 kg.) (a) What is the initial mass of the sample? (10 points) (b) How many nuclei in this sample decay in the time interval between f = 3.0 years and ( = 5.0 years? (10 points) 6.024 inyens