$3^x$ + $3^x$ + $3^x$ = ?

Explanation

B) $3^{x+1}$. Adding the same term three times is the same as multiplying it by 3, so the sum is 3 $\times$ $3^x$. Since 3 = $3^1$, the rule $a^m$ $\times$ $a^n$ = $a^{m+n}$ turns this into $3^{x+1}$. It is not $9^x$, which equals $3^{2x}$.