If the shapes are similar, the correspondent sides are in proportion:

Let's plug the values and solve for x:

Multiply both sides by x to get

The only feasible solution, though, is
, because it wouldn't make sense to have negative lengths.
Answer:
Step-by-step explanation:
4.2x+4.7=18.6
Multiple each term by 10
42x + 47 = 186
Collecting like terms
42x = 186 - 47
42x = 139
x = 139/42
x = 3 13/42 or 3.3
Karen's rate is 12 miles per hour
Jesse's rate is 8 miles per hour
Hope this helps =)