Lets look at the chart a little more closely to shall we?
It says 17.6% of Michigan are union workers. The whole state has 9,883,640 people (according to the 2010 Census Bureau)
Michigan QuickFacts from the US Census Bureau
The chart says at $1331/year more income and a ten percentage point increase in union workers the state would create $3,013,577,553 income in a year.
That means 27.6% of Michigan workers are now union in the chart x 1,331/year for the chart.
$3,013,577,533 divided by 1,331 = 2,264,145 union workers
2,264,145 union workers divided by the population of Michigan is 22.9%
22.9% is not 27.6%, it also means 22.9% OF THE WHOLE POPULATION IS UNION.
Here's a news flash, not everyone in Michigan works.
The whole chart is a lie.