I believe the answer would be 3 actually. The question asks how many gained "fewer" than 3 pounds. In math, there is inclusive and exclusive. Inclusive meaning that includes the number starting or ending number on the number line and exclusive meaning it does not include. Questions will always clearly state when an inclusive answer is required. Therefore the question would have asked "how many dogs gained 3 or fewer pounds." Since this is not the case the answer should exclude 3 and therefore be 3 dogs.
Plot the coordinates on a graph and join them to form a triangle. After doing that, you can count the length of each triangular side and find the sum of the 3 sides. That will be your answer.
