A tortoise ambled 39 centimeters east at a constant velocity, and it was passed by a frog hopping at 10 centimeters per second. It took the tortoise 5.0 seconds to travel that distance. What was the tortoise's velocity?
a. ( 7.8 , cm/s )
b. ( 39 , cm/s )
c. ( 10 , cm/s )
d. ( 195 , cm/s )