The plane PRS passes through the points P, R and S. So it contains the line RS. Also the plane QRS passes through the points Q, R and S. So it contains the line RS as well. Since both the planes contain the line RS, the line RS must be the intersection of plane PRS and QRS
The packing crate measures 3 feet by 12 feet by 7 feet (volume). To find the area of the smallest side, multiply the two smaller numbers
3 x 7 = 21
21 feet² is the area of the smallest side
hope this helps
