To simplify the algebra, assume that both the grey and the yellow lines are equal to 100 in 1980 and that the grey line is equal to 300 and the yellow line to 200 in 2018. (This is roughly in line with what the graph shows.) Then use this stylized version of the graph to answer the questions below. Let at denote the share of total income going to the bottom 90 percent in year t, that is, Y,90 t at Yt (a) Show that by definition 0