So,
In order to find numbers that are in between 3/8 and 6/7, Lucy must make common denominators first.
LCM of 8 and 7: 56
Multiply each fraction by the appropriate form of 1:


We can immediately see that any fraction with a numerator between 21 and 48 and a denominator of 56 will fit into the criteria Lucy needs.
The correct option is B.