Answer: None of the above
See below for the explanation
---------------------------------------------------------------
I'll go through the possible answer choices.
- A. If we tried a = 3, then 3^a = 3^3 = 27 which is not 81 that we want. This rules out choice A.
- B. Try a = 1 to get 3^a = 3^1 = 3 which also doesn't match with the 81. Cross choice B off the list.
- C. Try a = -1 to get 3^a = 3^(-1) = 1/(3^1) = 1/3. Still no, so we cross choice C off as well.
- D. Try a = 2 and we get 3^a = 3^2 = 9. Choice D is eliminated.
- E. Lastly, 3^a = 3^0 = 1 which eliminates choice E.
To summarize, choices A through E lead to results that aren't 81, so we must eliminate them. There's nothing left to pick, so your teacher must have made a typo somewhere. You'll need to ask her/him for further clarification.