What is the common denominator of 3/5 and 2/8

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)

Which graph represents the function f(x)=4[x]?

Out of the 180 students at a summer camp, 72 signed up for canoeing. there were 23 students who signed up for trekking, and 13 of those students also signed up for canoeing. use a two-way table to organize the information and answer the following question: approximately what percentage of students signed up for neither canoeing nor trekking? 72% 40% 54% 98%