So the graph shows the cost of the phone call on the y-axis and the length of the phone call on the x-axis.
The question ask is what is the least expensive per minute.
So your equation is cost/time.
Then you plug in the values of each point.
w=$1.25/2 minutes
x=$2/5 minutes
y=$2/10 minutes
z=$2.50/10.5 minutes
Solve each question-
w=0.63 (rounded)
x=0.4
y= 0.2
z=0.24 (rounded)
These values show the cost per minute of each point. So, in order the answer the question which one cost the least per minute you would select the lowest value answer from the question of each point. Which would be y.