Samuel's Middle School had a Week of Giving charity drive. The table below shows the number of participants per day.

Day Number of Participants
1 61
2 90
3 119
4 148
5 177

What is the constant of proportionality, or unit rate, for the increase in the number of participants?
14 people per day
45 people per day
29 people per day
35.4 people per day