b
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|. |
h |. | h
|. |
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b
Okay so I did my best to make a rectangle above. If you think about substitution, it pretty much means to replace. Like when your teacher leaves for the day so a sun comes in to replace them for the day. Since we're using 14 and 3 to replace b and h, your equation goes from b+b+h+h to find the perimeter, to 14+14+3+3.