To do this question, you have to convert meters to kilometers because you can't add two different units of measurement together! 
Remember that 1000m = 1km 
That means 220 m = 0.220 km 
(220 / 1000) 
Since Larry ran 0.220 km further than Leigh, add 0.220 km to 2.3 km 
0.22 km + 2.3 km 
=2.52 km
Hope this helps :)