Answer:
The number of cyclists on week 4 is 53.
Step-by-step explanation:
The mean is calculated by dividing the sum of numbers by how many number there are. In this case we have 4 weeks. The mean is 43, meaning in total, Rita had recorded

172 cyclists.
Now we can subtract the number of cyclists recorded on every other week, leaving the answer to the question.

Rita recorded 53 cyclists on week 4.