Which natural phenomena is the most best example of periodic behavior ?

What is the slope of a line that is perpendicular to y = 3x + 1

Use the graph of the sine function y=2sinθ shown below

Danielle earns a 7.25% commission on everything she sells at the electronics store where she works. she also earns a base salary of $750 per week. what were her sales last week if her total earnings for the week were $1,076.25?