Let´s remember that the formula to the position of a particula that moves in a line with constant speed is:

so, lets apply this formula for Annike, and for Celia:
First, for annika

Then, for celia:

Then, to know At what time will the two bikers have completed the same number of miles we need to equalize the two formulas of the position and solve for t:

so the answer is that they complete the same number of miles after 4.67 hours