To get the answer you must calculate 40% of 500 and 60% of 500 to see how many students for each candidate. To calculate the number of students who voted for Kellen you must multiply 40 by 500 an divide by 100.
40•500:100= 200.
Then you do the same with Robbie.
60•500:100= 300.
So 200 people voted for Kellen and 300 people voted for Robbie.
So the answer is that 100 more people voted for Robbie than for Kellen.