Do you mean an extraneous solution? I will tell you what I think. To tell if a solution is extraneous you need to go back to the original problem and check if there actually is a solution or if the solution is actually right. If not then it is extraneous.
You end up at the point (5, 5).
40 miles an hour
60 [minutes] * 60 [seconds]= 3600
22.5[seconds for 1/4 of a mile]* 4[ one mile]= 90 [seconds per mile]
3600/90=40 [miles an hour]