Choose the One Alternative That Best Completes the Statement or Answers

Choose the one alternative that best completes the statement or answers the question.
Solve the problem. Round your answer, as needed.
-Calculate an average rate of speed for $\mathrm{v}=4.7 \mathrm{mph}$ and $\mathrm{d}=6.4 \mathrm{mph}$ in the formula
$A=\frac{2 D}{\frac{D}{d}+\frac{D}{v}}$ .

A) $2.71 \mathrm{mph}$
B) $0.74 \mathrm{mph}$
C) Cannot be determined without additional information
D) $5.42 \mathrm{mph}$