Answer:
$3,628  per direct labour hour.
Explanation:
Total manufacturing overhead cost and total direct labour hours
Particulars                                       Dep 1             Dep 2          Total
Manufacturing overhead cost     1,360,000 3,560,000    4,920,000
Direct labour hours                       553,000     803,000     1,356,000
Plant-wide overhead rate = Total manufacturing overhead / Total direct labour rate 
Plant-wide overhead rate = $4,920,000 / 1,356,000
Plant-wide overhead rate = $3,628
Therefore, the Plant-wide overhead rate is $3,628  per direct labour hour.