18. Amelia tosses a coin, with the probability of landing heads up being $\frac{1}{3}$; Brian also tosses a coin, with the probability of landing heads up being $\frac{2}{5}$. Amelia and Brian take turns tossing the coins, and the first one to get heads wins. All coin tosses are independent. Starting with Amelia, the probability that she wins is $\frac{p}{q}\left((p, q)=1, p 、 q \in \mathbf{Z}_{+}\right)$. Then the value of $q-p$ is $(\quad)$.
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5