If labour hours are restricted in supply, which order should the company adopt when planning its production?

The contribution margin is the sales value minus all variable costs (direct material cost and labour cost).

• Product X: $\text{Contribution Margin}_{\text{X}} = \$1,200 - \$500 - \$400 = \$300$
• Product Y: $\text{Contribution Margin}_{\text{Y}} = \$1,200 - \$400 - \$600 = \$200$
• Product Z: $\text{Contribution Margin}_{\text{Z}} = \$2,250 - \$800 - \$450 = \$1,000$

This is found by dividing the contribution margin per unit by the labour hours required per unit.

• Product X: $\text{Contribution Margin per Labour Hour}_{\text{X}} = \frac{\$300}{2 \text{ hours}} = \$150 \text{ per hour}$
• Product Y: $\text{Contribution Margin per Labour Hour}_{\text{Y}} = \frac{\$200}{0.8 \text{ hours}} = \$250 \text{ per hour}$
• Product Z: $\text{Contribution Margin per Labour Hour}_{\text{Z}} = \frac{\$1,000}{3 \text{ hours}} = \$333.33 \text{ per hour (approximately)}$

1. Product Z: \333.33$ per hour
2. Product Y: \250$ per hour
3. Product X: \150$ per hour

Therefore, the company should adopt the production order Z, Y, X. This corresponds to option D.

The final answer is $\text{D}$.