3,6,9 means that width = 3, length = 6 and height = 9
to find the surface area it has several parts the top and bottom are equal to w* l
top and bottom = 2 l w
width sides = 2 w h
length sides = 2 l h
SA = 2 l w + 2 w h + s l h
SA = 2*6*3 + 2*3*9 + 2*6*9
SA = 36 + 54 + 108
SA = 198 units^2