(20 points) Find the s-wave phase shift do for the scattering of a particle with mass m on the spherically symmetric potential V(r) = Vo0(a - r) + Vid(r -a) (3) with positive Vo and Vi constants accompanying the Heavyside step and Dirac delta functions, respectively, for the energy of the particle E > Vo. Find the differential and total cross sections at low energies, i.e., ka