you have to find the area of all the sides. so there are 6 faces in total and two of them are going to have the same area. so you do: 8x5=40 8x3=24 5x3=15
then you add all of these up 40+15+24=79
then you times 79 by two since 79 is only ythe total area for 3 faces. 79x2=158cm2