At a walkathon, each participant competed either a 3-km route, a 5-km route or an 8-km route. 1/4 of the participants completed the 3-km route, 9/20 of the participants completed the 5-km route and the rest completed the 8-km route.

For every 1 km a participant walked, $4 was donated to charit. A total of $8208 was donated to charity.

a) What is the ratio of the number of participants who completed the 3-km route to the number who completed the 5-km route to the number who completed the 8-km route?

b) What is the total number of participants at the walkathon?