This is because the cost of the plan must be added to the cost of the lines to find the total cost. The equation for option (C) correctly depicts that<em> y </em>the plan, needs to be added to <em>x </em>the lines. This equation correctly shows the relationship between the two numbers.
The answer would probably be 18 degrees below normal because the absolute values of the rest are 8 not 18 which is the absolute value of 18 degrees below normal.
