To find the plantwide overhead rate, divide the total budgeted manufacturing overhead costs by the total budgeted machine hours.
\[Plantwide \space Overhead \space Rate = \frac{Total \space Budgeted \space Manufacturing \space Overhead \space Costs}{Total \space Budgeted \space Machine \space Hours}\]
Using the given data:
Total Budgeted Manufacturing Overhead Costs = $320,000 + $400,000 = $720,000
Total Budgeted Machine Hours = 2,000 + 2,500 = 4,500 MH
\[Plantwide \space Overhead \space Rate = \frac{720,000}{4,500} = 160\]
Rounded to two decimal places, the plantwide overhead rate is $160.00 per machine hour.
So, the correct option is:
$160.00 per mh.