Please solve below

3. (30 marks) In class, we covered the paper by Thomas Fujiwara on the introduction of electronic voting machines in Brazil and its effects on valid votes and turnout. In 1998, due to a limited supply of machines, only municipalities with more than 40500 registered voters in 2002. received those machines. In 1994, no municipalities had them, while all of them had them Recall Figure 2 from his paper: 0.9 co. 0.7 0.6 20000 40000 60000 80000 100000 Number of Registered Voters - 1996 - Valid Votes/Turnout - 1994 Election (Paper Only) . Valid Votes/Turnout - 1998 Election (Discontinuity) A Valid Votes/Turnout - 2002 Election (Electronic Only) FIGURE 2.-Valid votes/turnout-local averages and parametric fit. Each marker represents the average value of the variable in a 4000-voter bin. The continuous lines are from a quadratic fit over the original ("unbinned") data. The vertical line marks the 40,500-voter threshold. (a) (15 marks) Using this graph, explain how we can find a causal effect of electronic voting machines on the share of valid votes