Answer:
40.91%
Step-by-step explanation:
Duration perpetuity = 1.04/4%
Duration perpetuity = 1.04/0.04
Duration perpetuity = 26 years
Now, 17 = (Wz)*4 + (1 - Wz)*26
17 = 4Wz + 26 - 26Wz
26Wz - 4Wz = 26 - 17
22Wz = 9
Wz = 9/22
Wz = 0.409091
Wz = 40.91%
So, 40.91% of its portfolio should be allocated to the zero-coupon bonds to immunize, if there are no other assets funding the plan.