how do I do questions 1,2 and 3

Whirly Corporation's contribution format income statement for the most recent month is shown below: Required: (Consider each case independently): 1. What would be the revised net operating income per moth if the sales volume increases by 30 units? 2. What would be the revised net operating income per month if the sales volume decreases by 30 units? 3. What would be the revised net operating income per month if the sales volume is 6,000 units