General Idea:
The relationship between rate(R), distance(D) and time(T) given below:
[tex] R= \frac{D}{T} [/tex]
Applying the concept:
We need to make use of the formula to find Kelly's walking rate before and after her snack
[tex] Kelly \; Walking \; Rate \; before \; Snack:\\Distance \div Time = \frac{1}{4} \div \frac{1}{14} = \frac{1}{4} \times \frac{14}{1} = \frac{14}{4} = \frac{7}{2} = 3 \frac{1}{2} \; miles \; per \; hour\\\\Kelly \; Walking \; Rate \; after \; Snack:\\Distance \div Time = \frac{1}{6} \div \frac{1}{16} = \frac{1}{6} \times \frac{16}{1} = \frac{16}{6} = \frac{8}{3} = 2 \frac{2}{3} \; miles \; per \; hour\\\\ [/tex]
Option A isn't correct because before snack Kelly walking rate is not 4/14 miles per hour.
Option B is Correct, Kelly walking rate after snack is 2 2/3 miles per hour.
Option C isn't correct because it doesn't took Kelly 2 hours longer to walk 1/6 mile than it did for her to walk 1/4 mile. It took 1/112 hour longer.
[tex] \frac{1}{14} - \frac{1}{16} = \frac{1 \cdot 8}{14 \cdot 8} - \frac{1 \cdot 7}{16 \cdot 7} = \frac{8}{112} - \frac{7}{112} = \frac{1}{112} [/tex]
Option D isn't correct because 2 2/3 miles per hour is slower than 3 1/2 miles per hour.
Conclusion:
Option B is Correct, Kelly walking rate after snack is 2 2/3 miles per hour.