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Let's consider a rectangular prism with length 3, height 6 and width 12 .

To find lateral area, does it matter if we do $3(12) + 3(12) + 6(12) + 6 (12)$ giving us 216 then + 2(3)(6) for total surface area 252.

Or $3*12 + 3*12 + 6*3 + 6*3 = 108$ lateral area and then 612 + 612 that also gives us a total surface area 252 ?

Jean Marie
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The surface area of a shape is always the same, it does not matter how you find it, just as it doesn't matter if you use a pocket calculator, a computer, or a pencil and paper method to find 183+123. The answer will always be the same.

Fundamentally, there is some quantity you are measuring, and these are just different methods to measure it. We don't do these methods for fun, we do them because we want to know some quantity--the surface area, in your case. Don't understand the surface area as the answer to this addition problem, but instead understand it as the surface area (ie, how much cardboard you'd need to make this shape in real life) and try to understand the addition problems as ways to count this area.

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    So there isn't really no "correct" way to find it. ie. you have to find height and length and then width and length? –  May 13 '21 at 23:02