Scientific notation is used in science because the number can be vary from so much that using decimal is making it hard. The number expressed in form. Both number in the question is already in scientific notation. Then to multiply the number and keep it at scienfitic notation the calculation should be:
Step-by-step explanation: Since it's a rectangle, and not a rectangular prism, that means it's 2D. Length is the long sides on the top and bottom, and width is the shorter sides on it's left and right. So since there's two of each, just do 8.1 + 8.1 + 4.2 + 4.2 and you have your answer!