The difference in sales was 567 - 540 = 27. That's a 27 vacuum increase. Now we find what percent increase by finding what percent of 540 is 27...
x% of 540 = 27
540x = 27
x = 27/540
x = .05
Convert to percent by multiplying by 100 (move decimal 2 places to the right)
x = .05 x 100 = 5%
It is a 5% increase this year compared to last year.