Hi!
To find the gate that is used most often, we have to look at the gate numbers, and find which one appears the most (aka the mode).
The gate numbers are...
20, 18, 17, 19, 18, 18, 19, 20, 17, 18
Put the numbers in order.
17, 17, 18, 18, 18, 18, 19, 19, 20, 20
The number that appears the most is 18.
Hope this helps! :)