Part A.
We know that Chelsey runs 2.8 miles farther than Kyle, this means that she runs that amoun more or, in other words, that we need to add that amount to the number of miles runs. Therefore, the equation relating the distances is:
Part B.
To determine how many miles Chelsey runs if Kyle runs 4 miles we plug k=4 in the equation above:
Therefore, Chelsey runs 6.8 miles