How would I be able to determine if one of these is linear and non proportional?

Question

Select the best description of a real world situation where the relationship is linear and non-proportional.

Amanda borrows a flute from a friend for $5 per week and then pays $31 dollars per week for lessons.
Amanda buys a flute for $500 dollars and then pays $31.00 per week for lessons
or
Amanda rents a flute for $50.00 each month and then pays $31.00 per week for lessons.

Answer 1

All of these are linear, here are the equations.
a. Acost=weeks(5+31)
b. Acost=500+31*weeks
c. Acost=weeks(50+31)
all are linear equations, all will plot as lines on a graph of cost vs time.