Precalculus (6th Edition) Blitzer

An airline increases its price 300 dollar to x dollars. The dollar amount of the fare increase can be represented by $x-300$. For each 1 dollar increase in the ticket price, the airline will lose 50 passengers, so the decrease in passengers due to the fare increase can be represented by $50\left( x-300 \right)$. If the airline carried 5000 passengers per month before the fare increase, the number of passengers per month, $N\left( x \right)$, after the fare increase can be represented by the function, $N\left( x \right)=5000\text{ }-\text{ }50\left( x-300 \right)$.
Consider the statement: An airline increases its price 300 dollar to x dollars Earlier the price was 300 dollars, the price after increase is x. The increase in price is given by: $\text{New price}-\text{Old price}=x-300$ Now, for every 1 dollar increase the airline will lose 50 passengers. $\text{Total increase}=x-300$ So, the total number of passengers the airline will lose is 50 times the increase, that is $50\left( x-300 \right)$. If the airline carried 5000 passengers before the increase then number of passengers after the increase will be obtained by subtracting the number of passengers decreased from 5000: $N\left( x \right)=5000-50\left( x-300 \right)$