RSA Decryption from Simple Public Key Values
If you want to decode a message encoded with RSA, you need to get the private key. The "simplest" method is to find the primes $p,q$ with $n=p\cdot q$.

In your case, $n=18209$ is the product of the primes $131$ and $139$. Now, you can follow the value of Euler's phi function for $n$, which is $\varphi(18209)=130\cdot138=17940$.

The private key $d$ suffices the following equation

$b\cdot d\equiv 1\mod\varphi(n)$.

To get $d$ with this property, you can use the extended euclidean algorithm for $b$ and $\varphi(n)$, which produces $x$ and $y$ with

$1=x\cdot b+y\cdot\varphi(n)$

Now, the value $x$ is your private key $d$. In your case, I get $d=4621$.
To finally decode the message $m$, you have to compute

$m^d\mod n$