Option A, product x:

Cost per unit = $1.10

Initial Cost = $600

Total cost = 1.10x + 600

Option B, product x:

Cost per unit = $1.05

Initial Cost = $2500

Total cost = 1.05x + 2500

Now, what you are looking for is the number of units of product x where economies of scale begins to pay off. To do this, find the number of units for when the cost of Options A & B are equal.

1.10x + 600 = 1.05x +2500

.05x = 1900

x = 38000

When you are producing 38000 units, you will be indifferent to the two options because each costs the same. This can also be found by graphing the lines and finding their intersection, but it might be a pain to set the window right (ie: TI-83).

The other thing to look for is when to use which option. Assume you produce 0 units. Option A will be cheaper. This means that if you are producing 0 to 38000, you should use option A. Of course, this also means that if you are producing 38000 or more, option B should be used.