Each of those bones pictures are equal to 2 bones. The question is asking, how many more rib bones than skull and jaw bones combined, so you’re gonna have to do some addition and subtraction.
You take the number of skull bones, which is 1(2), and add that to the number of jaw bones, which is 0. Giving you a total of 2 bones.
Then you are taking the rib bones 3(2) and finding out that you have 6.
So with that information, you can find out that there are 4 more rib more than skull and jaw bones combines (6-2=4)