You are correct. Need to multiply 80 by 2. However, I think the answer is 160 & not 166 as you shouldn't divide the total area of the big rectangle by the area of 1 small rectangle to get total number of small rectangles. The remaining length after fitting small rectangles along the 100 cm is 4cm (12 12 12 ... until 96cm). The length of 1 small rectangle is 5cm. So can't fit any small rectangles in the space 4cm by 50cm. Hope you can understand my explanation

I am sorry for posting a wrong solution but I think you are correct although I can't understand the last part of your explanation.