Question 1010320
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Your formulation is not right.

You should start with the description of your subject, in this case, with the description of your solid. 


If it is regular square pyramid, say explicitly and directly:
"The total surface area<U> of a regular square pyramid</U> is 84 m(2) and it slant height is 4 m, how wide is its base?"
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So, edit and re-submit.