The correct answer is (d) (4s^2+19s+4)/(6s+8)
Easiest explanation: The term admittance is defined as the inverse of the term impedance. As the impedance is Z2(s) = 1/2s+1/(s+4)=(3s+4)/2s(s+4), the admittance parallel combination of the last elements is Y2(s) = 1/2+2s(s+4)/(3s+4)=(4s^2+19s+4)/(6s+8).