Answer
1990,
28%.
Work Step by Step
Between 1950 and 2010, the year during which the United States had the lowest lowest marginal tax rate is the point where the plot goes to its lowest point. As per the graph, it is 1990. So, 1990 is the answer.
Also, the estimated tax rate during 1990 is slightly less than 30%, i.e. 28%.
So, 28% is the answer.
