Here we can call the Fixed Expense x and the Variable Expense y.
Therefore, we see that x + 20,000*y = 570,000, while x + 25,000*y = 705,000.
This simply gives us two equations and two unknowns so we can stack them up to eliminate the x-value:
x + 20,000*y = 570,000
x + 25,000*y = 705,000
----------------------
5000*y = 135,000
y = 135,000 / 5000 = 27
Now just plug this back into either equation to get the answer:
x + 27*20,000 = x + 540,000 = 570,000
==> x = 570,000 - 540,000 = 30,000.
Answer B.
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