how do i do this?

Whirly's contribution format income statement for the most recent month is shown below: Required: Consider each case independently. You need not prepare a new income statement. Instead, use the incremental approach where possible. 1. What would be the revised operating income per month if the sales volume increases by 90 units? 2. What would be the revised operating income per month if the sales volume decreases by 200 units? 3. What would be the revised operating income per month if the sales volume is 10,800 units