Answer:
Contribution margin per unit = $450
Contribution margin ratio = 52.94%
Step-by-step explanation:
The calculations are given below:
Contribution margin per unit = Selling price per unit - per unit variable cost 
 = $850 - $400
 = $450
Contribution margin ratio would be
= (Contribution margin per unit) ÷ (Selling price per unit) × 100
= ($450) ÷ ($850) × 100
= 52.94%
And, the contribution margin income statement for August month is presented below:
 Contribution margin income statement 
 For the August month
Sales (425 motors × $850) $361,250
Less: Variable cost (425 motors × $400) ($170,000) 
Contribution margin $191,250
Less: Fixed expenses per month ($90,000) 
Net income $101,250