The break-even cost for Felicia is when:
20 x = 6,000 + 15 x , where x is the number of units that she must sell.
20 x - 15 x = 6,000
5 x = 6,000
x =6,000 : 5
x = 1,200
We can prove it:
20 * 1,200 = 6,000 + 15 * 1,200
24,000 = 6,000 + 18,000
24,000 = 24.000
Answer: She must sell 1,200 units to cover all of her costs. For more of units sold she will make a profit.