280 is 72% of what number?
1 answer:
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check the picture below, that's pretty much the same block, or "rectangular prism", with a width of 10, length of 5 and height of 1.
so anyhow, is really 6 rectangles stacked up to each other at the edges, so, we can simply get the area of each of those rectangles, add them up and that's the surface area.
front and back, two rectangles of 5x1
left and right, two rectangles of 1x10
top and bottom, two rectangles of 10x5
