What is the bicyclist's velocity at t=35s?

Since we are talking about the relation between the velocity and the time, the distance must be given.

Since no distance is given here, then I'll just tell you how to solve this question in terms of equations and you can substitute with the numbers you have.

The velocity can be calculated using the following rule:

velocity = distance / time

we are given the time as 3.5 seconds, therefore:

velocity = distance / 3.5