Final answer:
To determine the total stress at point A, the missing information is the soil density.
Step-by-step explanation:
To determine the total stress at point A, the missing information is the soil density. The unit weight of the silty soil can be used to calculate the total stress at point A, which is equal to the product of the soil density and the gravitational acceleration. The water content, shear strength, and soil type are not necessary to determine the total stress at point A.