AMC 12 2007b Problem 15

The geometric series $a+ar+ar^2\cdots$ has a sum of $7$, and the terms involving odd powers of $r$ have a sum of $3$. What is $a+r$?

$\mathrm {(A)} \frac{4}{3} \mathrm {(B)} \frac{12}{7} \mathrm {(C)} \frac{3}{2} \mathrm {(D)} \frac{7}{3} \mathrm {(E)} \frac{5}{2}$