Elgamal Protocol Failure I'm having a difficult time trying to solve this problem. 


  Suppose Alice uses the Elgamal signature scheme with  $(\alpha,
 \beta, p) = (2, 33384, 65539)$.   She publishes the two signed
  messages: $(m_1, r_1, s_1) = (809, 18357, 1042)$ and $(m_2, r_2,
 s_2) = (22505, 18357, 26272)$. Find $a$ by setting up and solving
  appropriate linear congruences. (I.e., don't compute the discrete
  logarithm of beta directly)


I know that $\beta = \alpha^a \bmod p$, which in this case would be $33384 = 2^a \bmod 65539$.  However, I have no idea how to use the messages to set up congruences to solve for $a$. Any help is appreciated.
Note the relation between $r_1$ and $r_2$
Infer the relationship internal variables need to have because of this
Write down the equations to calculate $(r_1,s_1),(r_2,s_2)$ and use the above relationship
Pretend the equations would be over $\mathbb R$ and solve the above system of equations for $a$
Now plug-in the values and actually perform the modular arithmetic
You now should have recovered the private key