An integer for a withdrawal of $50

An integer for a withdrawal of $50 is -50 because withdrawal means is to take something out. That would speak to a negative sign so simply add a negative sign to 50, it would be - 50.$50 represents 50 dollars which is the currency of United States.Then Withdrawals are always negative because you are taking away not adding in.

The best sentence is, Coral reefs are a very important component of the ocean’s ecosystem because they support sea life, such as crabs and sea turtles.  It's also the key sentence that explained the whole paragraph.  It touched all the topics or supporting details that follow.  

The following sentences explained the importance of coral reefs and the need for its protection to save marine life.