Percentage of votes received by Cindy = 55%
Number of votes received by Shawn = 423
Let us assume the total number of voters = x
Then
423 + (55x/100) = x
423 + (11x/20) = x
8460 + 11x = 20x
20x - 11x = 8460
9x = 8460
x = 8460/9
x = 940
So from the above deduction we can see that the total number of voters is 940. I hope the procedure is simple enough for you to understand. You can use this method in future for solving similar problems without requiring any help from outside.