Nestor R. answered 08/17/19
Statistician with a very good grounding in Algebra
Revenue R is the amount of money taken in by selling a product. Cost C is how much is spent producing the product.
You want to find where R - C >= 0. When R-C = 0 then revenue exactly matches cost. Otherwise when R > C then profit is made.
Solve for 85X - (60X + 660) = 0
85X - 60X - 660 = 0
(85-60)X - 660 = 0
25X - 660 = 0
25X = 660
X = 660/25 = 26.4
Revenue will exactly match Cost when 26.4 units of wire are produced. This is the break-even value of X.
When X > 26.4, R - C > 0 indicating a profit is being made.
The interval of interest is [26.4, oo). Note oo stands for + infinity