For this case we have the following equation:
d = v * t
Where,
d: distance
v: speed
t: time
Clearing the time we have:
t = d / v
Rewriting:
t = d * (1 / v)
We look for the value of d:
For t = 1, v = 75 we have:
1 = d * (1/75)
d = 75
Then, v = 15 we have:
t = 75 * (1/15)
t = 5 hours
Answer:
The value that is missing from the table is:
t = 5 hours