Given :
57% of the registered voters cast 273,600 votes in an election
So, the number of registered voters = x
So, 57% of x = 273,600
so,

So, the number of the registered voters = 480,000
In another election 60% of the registered voters cast 273,600 votes.
So, the number of registered voters =

in this case , the number will be = 456,000
The number in the first case is greater than the number in the second case
The difference = 480,000 - 456,000 = 24,000 votes