Answer:
The answer is: The break even level increases in 50 units.
Step-by-step explanation:
First we calculate the break even point without the increase in variable costs:
Break even point = fixed costs / contribution margin per unit
 = $4,500 / ($20 - $10) = 450 units
Then we calculate the new break even point with the increase in variable costs:
New break even point = $4,500 / ($20 - $11) = 500 units
 
The difference between the new and old break even points is: 
= 500 units - 450 units = 50 units