The numbers we want to compare are ther number of students that have rabbits and the number of students that have birds.
The number of students that have rabbits is in the column "Have Rabbits" and, since we want all of them, we get the value from the row "Total", so the number is 43.
Similarly, the number of students that have birds is in the row "Have Birds" and, since we want all of them, we pick the number in column "Total", which is 40.
So, the number of students that have rabbits is 43 and the number of students that have birds is 40. Since 43 is 3 more than 40, there are 3 more students that have rabbits that students that have birds.