Answer: A.) $4 per shirt
Explanation:
Slope of the graph is calculated as the ratio or proportion of chasing ein the y and x axis of a graph.
Slope(m) = [change in y / change in x]
One can draw a right angle triangle to meet the line of best fit provided in the graph to obtain the values for both the y and x axis.
HERE,
y2 = 120, y1 = 40 and x2 = 50, x1 = 30
Slope = (y2 - y1) / (x2 - x1)
Slope = (120 - 40) / (50 - 30)
= 80/20
Slope = 4
$4 per shirt