Twelve years after the melting of large glaciers, lichens begin to grow on the surface of rocks. Each lichen grows in a roughly circle-like shape. The following relationship exists between lichen diameter and age:

[[$ d = 7.0 \cdot \sqrt {t – 12} $]] when [[$ t ≥ 12 $]],

where [[$ d $]] is the diameter of the lichen in millimeters and [[$ t $]] the years since the ice disappeared.

a) Use the formula to calculate the diameter of the lichen [[$ 15 $]] years after the ice disappears.

b) Use the formula to calculate the diameter of the lichen [[$ 50 $]] years after the ice disappears.

c) If the lichen diameter is [[$ 45 $]] mm, find out by experimenting how many years ago the ice has melted from that place?

(Source: Programme for International Student Assessment, PISA)

Take a picture of your solutions and return it to the submission folder.

Answer: a) mm.

b) mm.

c) years.