Hey, what's this i don't understand this thx!?

Complementary goods. they go together, thats why one price increase and the others demand increases

C

If 1/5 of the students are in the football team and the class has 40 students, you need to multiple this numbers to know the exact number of students that form the team.40 x 1/5 = 8 studentsif 4 more students join: 8+4= 12 studentsto know the %: 40 students are equivalent to the whole class (100%). then 12 students are how much %? 40 students  = 100%12 students  =    x  %x= 30% of students are in the team.