Referring to the figure, determine which of the following graphs
best depicts this situation:  A vacuum repair shop charges a fixed
price plus a certain amount per half hour to repair a vacuum. Which
graph best shows how much a customer is charged based on how long the
job takes?
    a. Graph a                    c. Graph c	 
    b. Graph b                    d. Graph d
                                             
                                          
                                          
                                       