A right rectangular prism would have three pairs of identical sides. You need to find the area of each of these sides individually, then add them to find the total surface area of the shape.
The dimensions of the three unique of sides are length x width, width x height, and height x length.
So:
2(6 * 9) + 2(9 * 10) + 2(10 * 6)
2(54) + 2(90) + 2(60)
108 + 180 + 120
= 408 inches^2
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