Using Euler's theorem.. how can I get appropriate x..? The question is this...


  $x^{29}\equiv4\pmod{91}$. Note that $91 = 7*13$. Compute an integer $x$.


Since 91 is not prime number, I know I need to use Euler's theorem, not Fermat's. So I get 


  $a^{72} = 1 \bmod{91}$, $a \in Z_{91}^*$


I don't know what to do next...
This is RSA with $p=7, q=13$. First compute $d \equiv 29^{-1} \pmod {\varphi (pq)}$ and then $x \equiv 4^d \pmod{(pq)}$