The contribution margin is
the difference between

Contribution margin is the revenue remaining after subtracting the variable costs that go into producing a product. Contribution margin calculates the profitability for individual items that a company makes and sells.

Explanation:

the page presents four different kinds of threats that volcanoes pose and what to do before, during, and after an eruption.

the first successful, urban blues recording, selling more than 75,000 copies, was made in year 1920.

mamie smith recorded the first commercially successful example of the urban blues,   with the recording of “crazy blues”."crazy blues" was recorded on august 10, 1920, in new york city. within a month of the release of “crazy blues” it had sold 75,000 copies.