Answer
Y: 66.7%;
Z: 33.3%
Work Step by Step
Total overhead cost: 684,000
Using the plantwide overhead rate, percentage of the total overhead cost allocated to Product Y: $\frac{456,000}{684,000} \times 100 = 66.7$%
Percentage allocated to Product Z: $100 - 66.7 = 33.3$%