The height of a sunflower plant varies directly with its age. once it has sprouted from the ground, when a sunflower is 2 week old, it is 38 centimeters tall. when it is 6 weeks old, it is 114 centimeters tall. how tall is a sunflower plant that is 3 1/2 weeks old? a. 47.5 cm, b. 57 cm, c. 66.5 cm, d. 76 cm

The speed of the growth will be equal to the distance travelled divided by time taken. Therefore, because 6-2 = 4 and 114 - 38 = 76, it increases by 76 centimetres every 4 weeks. The speed of growth is therefore 76 divided by 4 = 19.

So, every week it grows roughly 19 centimetres. To find out how much it grows in 3 1/2 weeks, simply multiply 19 by 3 1/2 which gives 66.5 cm. 

The answer is C, 66.5 cm.