The following is a basic algebra practice exercise, and not a GMAT-level problem.
Which of the following expressions is equivalent to $$3^{x+2}$$?

Incorrect.
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Correct.
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$$3^{x+2}$$ is split into a multiplication of powers with base 3.
>$$3^x \cdot 3^2$$
Note that this is completely equivalent to $$3^2 \cdot 3^x$$ since the order of the multiplication does not matter. Also, since $$3^2 = 9$$, the expression above is also equal to $$9 \cdot 3^x$$.

Incorrect.
Don't fall for this trap. A "+" sign in the exponent does not mean that the powers *themselves* have been **added**: For a counter example, $$2^2 + 2^2$$ does not equal $$2^{2+2} = 2^4=16$$.
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$$3^x \cdot 3^2$$

$$3^{x^2}$$

$$3^x + 3^2$$