AMC 12 2009b Problem 15

Assume $0 < r < 3$. Below are five equations for $x$. Which equation has the largest solution $x$?

\textbf{(A)}\ 3(1 + r)^x = 7 \textbf{(B)}\ 3(1 + r/10)^x = 7 \textbf{(C)}\ 3(1 + 2r)^x = 7$$\textbf{(D)}\ 3(1 + \sqrt {r})^x = 7 \textbf{(E)}\ 3(1 + 1/r)^x = 7