Let us assume that
Speed of First biker = V1 km/min
Speed of Second biker = V2 km/min
Speed of Third biker = V3 km/min
Total time take by first biker = T1 min
Total distance = S km
Now as per the data given in the teaser, at a time T min
X1 = V1 * T ----> 1
X1 - 15 = V2 * T ----> 2
X1 - 18 = V3 * T ----> 3
At a Distance S Km.
S = V1 * T1 ----> 4
S = V2 * (T1 + 12) ----> 5
S = V3 * (T1 + 15) ----> 6
Thus there are 6 equations and 7 unknown data that means it has infinite number of solutions.
By solving above 6 equations we get,
Time taken by first biker, T1 = 60 Min.
Time taken by Second biker, T2 = 72 Min.
Time taken by first biker, T3 = 75 Min.
Also, we get
Speed of first biker, V1 = 90/T km/min
Speed of second biker, V2 = (5/6)V1 = 75/T km/min
Speed of third biker, V3 = (4/5)V1 = 72/T km/min
Also, the length of the course, S = 5400/T km
Thus, for the data given, only the time taken by each biker can be found i.e. 60, 72 and 75 minutes. For other quantities, one more independent datum is required i.e. either T or V1 or V2 or V3
