Priya covers a certain distance by her car at a speed of 21 km/h and returns at a speed of 17 km/h. What is her average speed during the travel?

A

$$18\frac{15}{19}$$ km/h

B

$$19\frac{15}{18}$$ km/h

C

$$17\frac{15}{21}$$ km/h

D

$$18\frac{19}{15}$$ km/h