1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution Hello, I am having confusion when calculating the first moment of area, Q, to solve for the shearing stress at point a in 13.9, I use the area which is above the point, but for 13.28 its to the right of the point. It seems they are both subjected to a vertical shear, so I don't think that has anything to do with it.