Quabbin Reservoir in Massachusetts provides much of Boston’s water. At the start of 2009 the reservoir contained 412 billion gallons of water. (a) If in January 2009 the amount (in billions of gallons) flowing into the reservoir is A and the amount flowing out is B , write an expression for the amount of water in the reservoir at the end of January 2009. (b) If in February 2009 the amount flowing in is 20 billion gallons less than the previous month and the amount flowing out is 12 billion gallons more than the previous month, write an expression for the amount of water in the reservoir at the end of February 2009. (c) Combine like terms to simplify your answer to part (b).

Look at this system of equations. -3x + 3y = 12 y = x + 4 the solution set of this system is best explained by which of these statements? a) the graphs of the equations are the same line because the equations have the same slope and the same y-intercept. the system has infinitely many solutions. b) the graphs of the equations are parallel lines because they have the same slope but different y-intercepts. the system has no solution. c) the graphs of the equations are lines that intersect at one point because the equations have the same slope but different y-intercepts. the system has exactly one solution. d) the graphs of the equations are lines that intersect at one point because the equations have the same slope and the same y-intercept. the system has exactly one solution.