The graph shows the girth of the trunk of a fir tree after different numbers of years: line joining ordered pairs 0, 5 and 1,12 and 2, 19 and 3, 26 and 4, 33 and 5, 40 what does the y-intercept of the graph represent? a)the girth increases by 7 centimeters each year. b) the girth increases by 5 centimeters each year. c) the original girth was 5 centimeters. d) the original girth was 7 centimeters.