Answer and Explanation:
The computation is shown below:
1) The contribution margin ratio is 
Contribution margin ratio = Unit Contribution margin ÷ Unit selling price 
 where, 
Unit selling price is 
= Total sales ÷ Number of units 
= $200,000 ÷50,000 
= $4 
And, 
Unit variable expense = Total variable expenses ÷ number of units 
= $120,000 ÷ 50,000 
= $2.4 
Now 
Contribution margin per unit = Selling price per unit - Variable cost per unit 
= $4 - $2.4 
= $1.6 
So, the contribution margin ratio is
 Contribution margin ratio = $1.6 ÷ $4 
= 0.4 or 40% 
2) 
 The net operating income is 
 In the case when the total sales increased by $1,000
Sales $201,000 
Less: variable expenses $120,600 
Contribution margin $80,400 
Less: Fixed costs $65,000 
Net operating income $15,400 
Prior increase in the sales, the net operating income is 
 Sales $200,000 
Less: variable expenses $120,000 
Contribution margin $80,000 
Less: $65,000 
Net operating income $15,000 
 So it increase by $400 i.e. 
= $15,400 - $15000
= $400