Answer : The retention time is, 20 min
Explanation :
Retention time : It is defined as the amount of time a compound spends on the column after it has been injected.
Formula of retention time is:

Given:
Distance from injection point to center of peaks = 10 cm
Chart recorded speed = 0.5 cm/min
Now put all the given values in the above formula, we get:

Retention time = 20 min
Thus, the retention time is, 20 min
I would assume so.
Given

, we can simplify the fraction to

Both would obtain the same proportions, so I don't see why putting a half cup of sugar would make things any different.
Hope this is the answer you are looking for.
The question is already answered.