The length of an object's shadow varies directly with it's heigt. if a can is 13 cm tall casts a shadow that is 7.5 cm long, a bottle that is 2.5 cm tall will cast a shadow that is approximately 14.2 cm long.

X = Can/Bottle height, y = Shadow length
x = 13 cm, y = 7.5 cm
x = 2.5 cm, y = 14.2 cm
I'm assuming your question is asking for an equation to model this. Since there are only two data points the only equation that can be made is linear
y = mx + c
m = (y2 - y1)/(x2 - x1) <- Let 14.2 be y2, and 2.5 be x2 (it is important)
m = (14.2 - 7.5)/(2.5 - 13)
m = 6.7/-10.5
m = -0.638
y = -0.638x + c
To find c we can sub any one of the two coordinates, i'm choosing (2.5,14.2)
14.2 = -0.638(2.5) + c
14.2 = -1.595 + c
14.2 + 1.595 = c
15.795 = c
So the final equation is y = -0.638x + 15.795

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