The total manufacturing cost per unit for Hadley under the ABC system is the sum of direct materials, direct labor, and total activity cost, which adds up to $63.
The total manufacturing cost per unit for Hadley under the Activity-Based Costing (ABC) system would be the sum of the direct materials, direct labor, and total activity cost. Under the ABC system, the total activity cost provided is $31. Therefore, the calculation would be: $23 (direct materials) + $9 (direct labor) + $31 (ABC system activity cost) = $63 total manufacturing cost per unit. Hence, the correct answer is $63 per unit.