The difference between fixed expenses and variable expenses is that fixed expenses do not change, regardless of how many items are produced. Variable expenses change based on the number of items produced.
An example of a fixed expense is the rent. The rent is always the same amount, regardless of production.
Materials would be a variable expense. You need enough material to make each item, so the more items you produce, the more material you need.
So angle CBD and ABC are a linear pair, which means that the two angles are supplementary (add up to 180°). Using this info, we can solve the equation for x as such:

Now that we got x, plug in 16 into x into 6x-60 and solve:

In short, Angle ABC is 36°
Quarterly is the answer I say