Answer:
The $ 4 per machine hour is the contribution margin per machine hour for the Lowell​ Lamp.
Explanation:
Since in the question two lamps : Bed-ford lamp and Lowell lamp information is given .
Based on the information mentioned in the question, First we have to calculate the contribution margin per unit. Than we are able to calculate contribution margin per hour.
The computation for Lowell Lamp is given below
The contribution margin per unit = Sales per unit - variable cost per unit
                           = $38 - $22
                           = $16 per unit
Since, contribution margin per unit is  $16 per unit. So, now we calculate contribution margin per machine hour  which is equals to
Contribution margin ÷ machine hours for Lowell lamp
$16 per unit ÷ 4
= $ 4 per machine hour
Thus, the $ 4 per machine hour is the contribution margin per machine hour for the Lowell​ Lamp.