A. 99
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Explanation:
The question is asking to find the value of x that makes the equation 3x = 291 true. To do this, you can use substitution by trying each value in the set {97, 98, 99} for x and checking if the resulting equation is true.
Starting with the first value, if you substitute x = 97 into the equation 3x = 291, you get 3(97) = 291 which simplifies to 291 = 291. This is not a valid solution because it doesn't make the equation true.
Moving on to the next value, if you substitute x = 98 into the equation 3x = 291, you get 3(98) = 294 which is not equal to 291, so this is also not a valid solution.
Finally, if you substitute x = 99 into the equation 3x = 291, you get 3(99) = 297 which is also not equal to 291, so this is not a valid solution either.
Since none of the values in the set {97, 98, 99} make the equation 3x = 291 true, the answer is D, none of these.