It is required to find the number of points Darren won round 3 by.
From the table, it is given that Darren had 15 points in round 3, and Sherri had -10 points.
To find the number of points Darren won round 3 by, find the difference in their points for round 3:
Hence, Darren won round 3 by 25 points.
Explain to Sherri that Darren won round 3 by 25 points and that this can be found by subtracting his points for round 3 from Darren's points from round 3.