bryn has a stack of photos measuring 12cm wide and 16 cm high. he wants to display them on a large rectangular poster in such as
way that all photos are equally spaced on each side, including at the edges of the poster, as illustrated. Bryn wants to display 9 photos (with longer side vertical) in 3 rows of 3 photos each with 2cm spacing around each photo. What are the dimensions of the poster?