18. Each of the fractions $\frac{2637}{18459}$ and $\frac{5274}{36918}$ uses the digits 1 to 9 exactly once. The first fraction simplifies to $\frac{1}{7}$. What is the simplified form of the second fraction?
A $\frac{1}{8}$
B $\frac{1}{7}$
C $\frac{5}{34}$
D $\frac{9}{61}$
E $\frac{2}{7}$