This video is a review of how to add whole numbers vertically. Once you see the question, pause the video, complete the question on paper, and then use the video to verify your answer and thinking process.
This video is an introduction to isolating variables to solve for the missing value. In this case, the problem involves the principle of calculating the average. When you see the question, pause the video, and try to solve the equation on your own. When you are done, watch the video to verify your answer.