What work am I supposed to do I have to do the work or I will get it wrong !

Cthe residual plot for model 1 has a non random pattern and is a good fit for the data

Idon’t understand what you’re asking..

Period is the time it takes for one “cycle” to complete. in the parent sine function, period is 2*pi since sin(0) = 0, sin(pi/2) = 1, sin(pi) = 0, sin(3pi/2) = -1, and sin(2pi) = 0. at that point, the sequence repeats itself. i’m not sure if your graph is similar to the sine function since you didn’t provide a picture, but you can find the period by looking at a graph.

4x 20 is 80 but if ther machine is broken then there is none you have to redo the test