As the sea floor of the atlantic ocean spreads, the african plate moves eastward. over the last 100 million years, the plate has moved approximately 2,100 kilometers. how many centimeters per year does it move eastward?

The correct answer is - 2.1 cm per year.

In order to get to the result of how much the African plate has been moving annually over the last 100 million years, we should first turn the kilometers into centimeters:

1 m = 100 cm

1 km = 1,000 m

1,000 m = 100,000,000 cm

2,1  x 100,000,000 = 210,000,000 cm

We got to the result of 210 million cm of total movement. Now we have to divide the number of cm with the number of the years in which the plate has moved that much, which is 100 million:

210,000,000 / 100,000,000 = 2.1 cm

So we get a result of an average movement of 2.1 cm per year pf the African plate during the period of 100 million years.

81 is a composite number.