All of the equations are the same, I'm not sure
Well if you start at zero for the cost and go to $10 which would represent the cost of one flip-flops and it goes up at a 10 to 1 ratio so your linear function for that would be f(x)= 10x 10 being the cost per production of flip-flops and x being the number of flip flops.
then you would have the a $15 dollar sell rate or which would be a $5 extra rate. so then as you graph what would you get?
The slope of the ramp would be 5/9
Think your answer would be C or D.
it's your choice to decide between those two now.