Answer:
5.5 seconds
Explanation: You can either use a proportion or simple division for this, depending on how it is requested.
Proportion
14 mm/1 sec = 77 mm/x sec [cross multiply]
14x = 77 [divide 77 by 14 to isolate the x]
x = 5.5 seconds
Simple Division
77/14 = 5.5
