We can calculate the net yard as adding the two events in respect to the same reference value.
The first event is gaining 14 yards, so we have a=14.
The second event is losing 20 yards, which according to our reference is a negative value: b=-20.
Then, we can calculate the net effect as:
This correspond, as it has a negative value, to a loss of 6 yards.
Answer: the total change is 6 yards lost.